Depends on a lot of things. Are the teeth worn down? Those can get expensive quick. What kind of teeth does it have? How are the bearings for the rollers? How many rollers does it have?
I got a 6' gill with double rollers for cheap ($200), the tines are worn pretty round, which could be sharpened I suppose, and the rollers have bad bearings. I have used it the way it is- it works ok especially on soft soil, but have new bearing and plan on painting the thing and doing the bearings at the same time. I may make/buy new tines as well. So was it a good deal? I am not sure, but usually ones around here in better shape go for around a grand or more.
I think they are awesome, especially if you have fairly soft soil to begin with. I am not extremely experienced but I have not seen another implement that will do what a pulverizer will do in one step in the right soil. Hard soil needs be broken up first for it to be the most effective. Best to plow/roto-till/disc first, otherwise it will take many passes before it really starts doing anything. Of course that could because the teeth on mine are getting pretty rounded.