Re: 540R with a rusted edge
Those are great guitars and if you can get one for a reasonable price (say $400 or less), you'll be happy. They sell in the auctions for anywhere from $300 up to $600, depending on features and condition.
The rusted trem parts are common and everything usually works fine despite the rust. Sometimes simply wiping them down with a lightly oiled rag and then a clean cloth is sufficient. On other ones, I've had to disassemble the whole deal and soak/clean each part individually. Edge trems have some teeny parts so you have to pay attention, but it's not difficult. Maybe take a few pics as you go along so you can remember how to reassemble and get the intonation back close to where it belongs.