Again, it was not me that was asking the question and I believe OP made it quite clear that he wants (1)a film camera that (2)takes M lenses and (3)costs less than $500.
So, now that we (hopefully) know the requirements, what are the options? That it won't be a new camera should be pretty much clear by now...
With those requirements there are I think only three options
1/ Get a film camera with a considerable crop from the list in my previous post, though I suspect there are no suitable adapters for them produced.
2/ Be very lucky, film cameras with M mounts occasionally sell for under $500, but most of these have known issues. A badly listed camera MIGHT work fine but escape everyone else's attention.
3/ Carry out a DIY modification - not a simple operation but there are those who could pull it off.
I wouldn't consider any of these to be good options to attempt, so refining the parameters may be needed.