Agree that spindle should be relatively quiet and no obvious vibration when you touch it behind the wheel guard.
The Boyar Schultz certainly is a well made machine (I own one), and was copied by lots of importers, so lots of clones out there. Not much in way of parts available, but typically don't need many as can get/make most of them. Harig, Chevalier, Brown and Sharp, Doall and others are very similarly well made units. Best I ever ran were the Mitsui / Okamota ball way machines, hands down.
Most them will have worn ways and screws in middle of travel, anywhere from light to heavy wear. Best to get an idea of how much it has before you take it home, and compare that to what you want the machine to do.
Not sure what the market is like near you, but around here the Boyars go for same as you, others maybe 1000-2500, and Mitsui / Okamota maybe 3500-5000. Much as I wanted a Mitsui, I could not justify the cost.
I paid 500 for mine, spindle reasonably quiet, rubber dust guards split, .020 backlash, and extremely dirty, but 15 miles from home with free loading onto my trailer. I have another 500 into it for all new oil metering valves (old grinders valves are typically clogged), new rubber guards, new bellows for the cross screw, missing wheel guard, etc. Also added now oil marks to table, cleaned out the lube tank, and cleaned it all up (lot of work). I have done a fair amount of work with it, and seems reasonably accurate, can usually get within .0002, good enough for home use.
No matter what you buy, will most likely need 200-500 to get it into good running shape. All just depends on what you want it to do.