I wouldnr pay more than 500 for a used one, I see better deals than that on ebay and the classifieds, not that it isnt worth more than that, its just that with so many being sold there are some good deals on used sovs. I wouldnt be afraid to buy even a well used one a couple years old for the right price, I never had any problems with mine in the 4 years I had them and it still works fine, also all the models give the same performance so the newest ones wont get you any more than the others.. If it were me I would be looking for a XS or XS II with Sunray Meter, and if it had multiple coils or sunray probe that would be even better.. I have seen XS's with SR DTI meters for as low as 300-350 bucks... now thats a deal!