If it's a Stingray original version, it is pretty expensive as these units are getting pretty old. Stingray original doesn't allows you to swap coil, so it's a major inconvenient.
If it's a Stingray II, this version allows you to swap coils. But these units are also getting pretty old and I track down the price of the last few units sold on Big-bay and they sell for 325 to 360$ max. They often comes with a new shaft and because of this, it is difficult to evaluate how the machine have been used. They are has good as the Tiger in my opinion, but they are getting old now. I have a Stingray II that I used since year 2001 and It's my main fresh water machine, i would never sell it as it is very sensitive on gold, but on the other end, the Stingray is not that sensitive on silver (compare with a Tejon or a Sovereign). If you adjust the discrimination properly (around 2.5), you will be able to ear a broken sound over rusted bottle caps and other rusted items, it's pretty good for that. Gold, silver, nickel, copper and aluminium will sound lound, many times I can't predict what is under my coil, so I have to dig a lot of trash. Overall, if you can pay around 325 to 350 max, it's a good buy, you may have to have it recalibrate by Tesoro, but you should be satisfy. I always used my Stingray II with a 12 x 10 land coil, since I put on, I never removed it.. just to say.
I never own a Tiger, but my bodies Martin and Luc are saying that they are very similar to the Stingray II. The good side is that this units are much more recent and you may have less issues on the long run. I think it may be worthed to spend $100 more and get a Tiger, which should cost you between $400 to $450 max on the used market.
At 400$, the Stingray of you friend might be a little overprice, but I didn't see it and its excellent conditions may justify the price. There is a guy that had one for sale not long time ago, he had both 8 and 10" coil and an extra land coil adapter. I spoke with him a little and i think he had a very good unit and his selling price at 425$ was in his case totally justified.
Good luck..