It's D750 priced, but good value for something with the D810 sensor.Pentax, while a bit weird, is really good value wise. There's some weird ergonomic quirks (They have a really weird setting dial that makes absolutely no sense to me), but I know their K mount 50mm 1.4 is some good stuff -- I bought my mom one to go with her K1000, and got kinda jelly when I was testing it on my A7 to make sure there was nothing wrong with it. And their Full Frame was like what, $600 or some shit? Do I remember that right? I remember it was stupid cheap for what it was.
Pentax has plenty of old film bodies. The K1000 is the most well known, basic fully manual and really popular with students back in the day. KM had slightly more features and the KX is the step up with mirror lock up and shutter speed showing in viewfinder. K2 was the high end and first with automatic shutter speed.
MX is the KX successor and followed the M series trend of being much, much smaller (SMC-M lenses are also much smaller than preceding SMC lenses, sometimes called SMC-K). It's also got automatic shutter speed. ME is the budget model and is locked in automatic shutter speed or aperture priority. ME Super is the same except for a manual model where you use buttons to change shutter speed versus the old dial. MV and MG are even cheaper versions of the ME.
LX is probably way too expensive, but was the highest end model in the 80 and one of the first cameras I know of that boasted of weather sealing. It's known for some unreliability tho with shutters locking up, but that can be common on older cameras. Make sure you check the shutter through all settings and speeds before buying one. There's nothing wrong with firing the shutter with the back open to check if it opens all the way etc.