To start with, I am posting the very first point that all should remember.
A lot of times, one would find vintage turntables at different price points. A lot of the price points are referenced using online resources like eBay, Audiogon, etc. A lot also has to do with the reviews written about the model in contention, over the internet. The more a turntable is found to be used in an audiophile project, the more valuable its perceived to be and higher the price.
Well, in my opinion and from experience, the above is absolute "Rubbish"!!
A vintage turntable is not valued based on its rarity, its popularity or its reviews. A vintage turntable is valued based on its condition. Condition includes the following (not exhaustive and not in order):
1) Originality vs Modded
2) Cosmetics, plinth condition, tonearm clip, dustcover
3) Interconnects and ground terminal
4) Signs of wear and tear
5) Original parts, headshell, tonearm and related components, platter, turntable mat, motor, idler (for idler turntables), belt (for belt drive turntables), etc
6) Quality of cartridge and condition of stylus (having the best cartridge is the world given away with the TT, but with a broken stylus is worthless, a new stylus costs almost as much as the new cartridge itself)
7) Operating voltage (and pulley for idlers)
8) Functionality, absolutely everything should be working as intended
9) Ownership history
10) Service history