While your (pick one - Parent/Spouse/Bank Manager) was pretty understanding about your $500 autofocus SLR, and the Macro lens made a good birthday present, there is no way that you are going to slip a 'Blad or even a Pentax 67 in unnoticed. And you're lugging around a ton of gear already. What you need is a camera that makes big negatives, has a sharp lens, doesn't weigh much, and won't blow the budget. What you need is a Rollei TLR .
Rollei TLR's use 120 (and sometimes 220) film to produce an image of just under 6cm square. There are a variety of models on the used market today, from Rolleicords of the 50's to the latest 2.8 GX (also available new at B&H for $3,550, but that's another story...). Prices run from $150 for user 'cords to upwards of $1000 for a clean, late 2.8F.
The Rolleicord Va was a 50's economy version of the Rolleiflex (in other words, the N50 of it's day). It has no meter, the finder is fixed (the later Vb has a removable finder), and it only takes 120 film. It's very light - about the same as my Nikon FE2 and 50 f1.4. The lens is a 4 element, f3.5 Zeiss Tessar or Schneider Xenar - no match for the Planar, but stopped down to f8 it is capable of producing outstanding results. There is a built-in leaf shutter with speeds of 1 second to 1/500, and B. Both the taking and viewing lenses have the Rollei Bay 1 bayonet for mounting accessories. The shutter speed and aperture are controlled by levers around the taking lens. They are locked into one EV setting - moving the aperture closed one stop slows the shutter speed one stop. Pushing the aperture lever in releases the lock, allowing the two controls to be used independently. I am not sure if this is a help or a hindrance - this feature seemed to come and go on various Rollei models. Shutter and aperture settings are visible at waist level with a little "wiggling".
Viewing is through the waist level finder with flip up magnifier - it's not very bright, but no worse than an early 80's 'Blad with 45 degree prism I have used. Using the magnifier and wearing a baseball cap outdoors (to provide additional shade) helps significantly. My focusing screen has grid lines and no split image - I found this combination to be ideal. For landscape shots I use the hyperfocal principle via DOF markings on the focusing knob (going up one stop for a safety margin) so the dark finder is not a problem. Parallax compensation is automatic, with a moving mask under the focusing screen. Another alternative is to fold down a square panel in the hood to create a open "sports finder" for eye level use - it's simple, but it works.
Film advance is via a knob, and the shutter needs to be cocked separately. There's also a cable release socket, double exposure capability, self-timer, and a flash PC socket with X and M sync.
The Rolleiflex 2.8F was the last of the dinosaurs. It came with or without a coupled selenium meter. Mine has the meter, which is surprisingly accurate and can be adjusted 3 stops for filter correction via a dial on the left side. The finder is removable and the focusing screen interchangeable. Mine takes 120 film, but some models took 220. It is heavier than the 'cord, feels more solidly built, and the controls are extremely smooth - the 'cord feels much more substantial than an N50 or a Rebel G, but the 2.8F is in another league. The lens is a 5 element, f2.8 Zeiss Planar (the Schneider equivalent is the Xenotar), which unlike the Tessar is outstanding wide open. Like the 'cord there is a built-in leaf shutter with speeds of 1 second to 1/500, and B. The taking and viewing lenses have the Rollei Bay III bayonet, for which accessories are larger and (unfortunately) substantially more expensive. The shutter speed and aperture are controlled by knobs which fall under your thumbs when cradling the camera - on my 2.8f they are not linked. Shutter and aperture settings are visible at waist level through a small window on top of the taking lens.
Viewing is through the waist level finder with flip up magnifier. The screen in mine had a faint grid as well as a center split image, but I found the split image to be of little use - it's hopeless at waist level, and if you are using the magnifier you don't need it. I replaced it with a Beattie Intenscreen (plain with Grid - $119 from B&H) and the improvement was substantial. Parallax compensation is automatic, with a moving mask under the focusing screen. A flip down sports finder is included, with a clever twist - a small glass window is mounted on the back of the finder, about a half inch below the standard sports finder window. This shows an upside-down , non-reversed, magnified image of the focusing screen, via a mirror mounted on the underside of the flip down panel. This allows you to frame an image, slide your eye down to focus, and then return your eye to the sports finder to shoot. Sounds a bit cumbersome, but it works. There's also a cable release socket, self-timer and a flash PC socket with X and M sync.
Film advance is via a fold out crank - turn 180 degrees to advance, turn back 180 degrees to cock the shutter. There's also a cable release socket, self-timer, double exposure capability, and a flash PC socket with X and M sync.
I am a big fan of composing on a tripod using the waist level finder, but when I got the chance to get a Rollie 90 degree prism cheap (20 GBP from a dealer on Portebello Road!), I couldn't resist. It snaps in place of the waist level finder on the 2.8F and provides an unreversed view. However, controls that were so ideally placed at waist level are very awkward at eye level. To make it work you need the Rollei Pistol grip, which slides onto the base of both the 'cord and 2.8F with one of the most elegantly designed mounts I have ever seen. The pistol grip (you can see a picture of both the grip and prism at B&H) has a trigger activated cable release and flashgun mounting point. I got mine for 25 GBP - you can hunt around for an old one, or get a new one for $282 (!). You are now set to impersonate a '50's reporter, and if you can grow a third hand you can probably operate at a pretty good clip - one hand to hold the grip, one to focus, and one to wind the film (the film advance and focus knobs are on separate sides of the camera).
For close up work the Rolleinar close up lens sets are available in three strengths. Each set has two lenses - one for the viewing lens, one for the taking lens. The viewing lens has a built-in prism which adjusts for parallax, making handheld parallax-free close-up shots a snap.
I bought a Bay 1 to 52 adapter and now can use all of the filters from my Nikons on the 'cord. I am still looking for a Bay 3 adapter, but in the meantime I just hold filters in front of the taking lens. For flash work any tripod socket mounting bracket will work. Rollei's take a standard cable release.
For the price of a Hassy back, you can put together a nice kit consisting of a Tessar lens TLR, tripod, lens shade, incident meter (I use a Gossen CDS Super Pilot), small bounce flash (mine is a Vivitar 2500), cable release, close up lenses 1,2, and 3, polarizer, 81a, red, green, orange and ND grad filters. It will fit in the smallest of bags and bring home some outstanding images. A Rollei also makes a good addition to a full 35mm setup - it will fit into the same area in a bag as a 180 f2.8 lens (something that the much larger Mamiya TLRs, with their interchangeable lenses, bellows focus, and dual focusing knobs, will not do).