A new Mars hydro 900 is the same price. Add shipping and subtract a discount code and your better off buying new if you ask me. Or you could get a new 700 Mars II for $300.
You could ask get ahold of Sara on this forum and you can get a deal that way. I just ordered a 1200w and a tent for my veg room.
Echo ... Sara has been very helpful with several of my MH purchases. I would surely buy new for that price, $150 is about the most I would pay for a used MH 600watt.