Sub $500 for me would be Nikon FM2, with the 24mm f/2.8 AI-S and the 135mm f/3.5 AI-S. I feel like if I had to go out right now and build a kit for that price this is what I'd actually buy.
Sub $1000, this might be a stretch to include under Contax, but the Contarex Bullseye/Contarex I - with the 50mm f/2 Planar and the 135mm f/3.5 Sonnar. They're very extravagant cameras and I love them for that. I finally got to briefly hold one in person a little ways back and they're very interesting in person. Not really like any other camera I've held.
Also honorable mention in the sub $500 category just because I have such an affinity for them, Konica Autoreflex T3 with the 35-100mm f/2.8.
This thread makes me think it'd be kind of fun to do a camera version of the $2000 challenge that they do over on the Grassroots Motorsports forum. Like, what's the best setup you could build and actually do a photo challenge with for under $50?