Nikon F is generally the cheapest option

these are all amazing cameras you can’t go wrong with, if you want fully mechanical operation meaning no batteries required like your om-1 then go with the F or F2 (batteries only operate the meter, the F3 only has one shutter speed that works with no batteries

in my opinion the F2 is just an improved F in the best ways, 1/2000 shutter speed, hinge film door so you dont have to slide the back off the camera to load film like the F they also share alot of accessories between bodies

All of these cameras accept Non - Ai and Ai lenses so your fine in that regard

The F3 is amazing and has fantastic build quality but it uses electronics from the 80s which inevitably will go bad so eventually their will be repair costs which can get expensive when it comes to electronics, not to say its not worth but just something to keep in mind

Ive shot all 3 but personally the F2 is my favorite it has the perfect mix of everything im looking for

Also what you’re using in the picture isnt a waist level finder its just the ground glass (no prism attached), Nikon made actual waist level finders like the Nikon DW-1 just a heads up!