If you want to adapt old lenses don't get a Canon or Nikon unless you want to get into their mirrorless cameras but they're out of your budget.
Get a Sony if you don't mind vignetting. Maybe the later models don't vignette as bad, look it up? When I was diving back into digital I bought a Sony A7 so I could just adapt my film lenses. They vignette, as I've shown, but I don't mind it. I've had my Sony for 6 years and never felt the need to buy a Sony lens.
Don't be afraid to get a non-FF camera. Dont believe the FF hype. Getting an APS-C Sony or a Fuji will negate a lot of the vignetting issues you seem to have a problem with. I love my Fuji despite it being aps-c. I will not be using my A7for shooting anymore because I like the Fuji better and fact I don't need to post process images from it. This is all personal prefence.