I think most b3's range in the price range of 4000 to 8000 that is reasonable unless you get one of the digital ones they are over 10,000. I think 15,000 to 20,000. You may also want to know if a used one is solid-state. That means they took the insides and made some of it with new digital stuff I think that means they took out the tubes. I think one thats solid state may save electricity but may not sound as warm as a tube b3.
Although I have heard the insides of all b3's are the same seems like to me the b3's with the square drawbars sound warmer and the one's with the rounded drawbars sound more of a distorted gritty sound. Then there is the leslie if the leslie is a 147 the leslie spins as soon as you turn it on but on a leslie122 there is a delay before it comes on. I think the 122 sounds better even though I have heard they are the same internally also but I'm not sure. Then you also have the problem with percussion the b3 may or may not have it depending on the year it was made. Some come with the trek box to add percussion or have it built in on the right. You can come out cheap though buying a A100 or a C3 I think. You would have to see hammondman about that. I used to work at a music store with Hammond C3 and they bought one from this lady for $1000 then jacked up the price on it. You may be able to find one in a trader type paper but you might have to have someone check it out. There is also a website in florida that sells them but I done remember the link so you can do a search on it.