Best I've seen recently available that meets that criteria is in the $850-$1000 range. Every now and then you'll see a bargain if it happens to already be sprung for your preference and not need a refresh.Gen 4 bike. Shocks with <1000 miles and recently serviced. Yes, with correct springs...
you need to be very careful with used ohlins shock prices... they have multiple versions of the ttx, and the older non GP units are a great shock but, people try to get new gp 2 or 3 pricing out of them, when they are clearly not the latest and greatest technology.
oh, and NEVER BELEIVE THE SHOCK WAS "JUST" SERVICED, WITHOUT FULL DOCUMENTATION, FROM A REPUTABLE SHOCK SERVICER. the sellers "always say that, it was refreshed", then you find out different when opening the box.
Personally, unless it was close to 50% off retail or better, I wouldn't entertain used, especially if it is not a gp 2 or better. you will still need to service it for piece of mind, and more than likely need the correct spring for your bike, weight, and track/street specification.
your results may vary. Ski