The only decent machines that one can occasionally find for quite low a price is the Otari 5050 because it is a professional machine that was built in vast numbers and is extremely rugged. But, because it is a professionally used machine, most of them on the market have been heavily used. A friend who serviced machines likes them because of how rugged they are and they are relatively easy to fix. He said that the basic build is even better than Studer machines. The amount of work needed to get a machine really up to snuff is considerable, and aligning heads and calibrating machines requires a lot of skill and specialized gear and expensive alignment tapes, so it is not something that is a do-it-yourself project even if you are good at it.
Many great sounding machines, like the Technics 1500 and 1700 models, are very much in demand and command high prices. But even ones in good working order can be ticking timebombs. The Technics machines are filled with cheap Panasonic electrolytic capacitors that WILL start to leak and the leaking electrolyte is highly corrosive and can destroy circuit boards. That means anyone owning such machines should spend a lot for preventive parts replacement if they hope to keep those machines alive.