I agree that the M3 and R3 are far from ideal for use with a 28mm lens (widest frames are 50mm and 40mm respectively). The M2 has 35mm frames, and if you don't wear specs you could use the full frame to approximate 28mm (which I do occasionally with mine). And the CV R2 also has 35mm frames, so I guess you could do the same with that.
The R4, of course, has 28mm frames (its widest being 21mm), but for regular (mainly?) 28mm use, I think its VF is too wide - I have one, but I use it primarily with a 21mm lens. My choice when going out with a 28 (which is one of my favourite FLs) is an M6, which has a 28mm frame, but one of those would break the $700 budget. Some of the M4s have 28mm frames, but I don't know what prices they go for.
If an M4/M6 was above budget and I mainly wanted to use a 28mm lens, I'd probably narrow the choice down to a new R2 or a used M2, and I'd almost certainly go with the latter (but I'm biased as I already have one, and I think the M2 is probably the best camera ever made).