I wouldn't mind a Prince NEOS 1000 also. they are great machines. Two things you need to look out for when buying a used one:
1. how many racquets were strung on it? If its more than 10,000, then perhaps $750 is a bit high of a price.
2. You'll need to invest in a gamma calibrator. cranks need to be calibrated, and it probably doesn't come with one.