pianomart.com for second hand pianos, which give you an idea of prices and what's out there.
First of all, don't pay list price. For some mysterious reason most car and piano sales people give you a price entirely above what they are willing to sell to you. If you find one that up front gives you a reasonable discount, this is a person worth talking to. Let the various sellers from whom you are considering buying know what other options and prices you have available.
Second, just as with cars, there are loads of technicians that have no idea what they are doing. Judge by the state of the other pianos they service or offer for sale. Try several, you will be able to tell right away which ones are the good ones.
Brian, wouldn't you agree that for the most part the pianos in
www.pianomart.com are significantly overpriced? That's my impression. Exceptions, of course.
Mikeyg, if you have a $20K budget, which is quite respectable, and depending how much space you have available, I would actually seriously consider buying a new piano from a reputable technician (my favorite guys are at Pianocraft, in Maryland, just in case you are curious; I bought from them and they have been great to me - top notch service). I don't recall whether you have told us where you are located, but if you are in USA east coast you have many nice choices.
I would recommend you check out Estonia pianos, particularly the 190 (I think that's about 6'3 or so). Very nice instruments. i think they are within your budget; not sure, though.
Nothing wrong with used pianos, but if you are spending a lot of money, it would be nice that the piano would be in top shape and used pianos rarely are. The scenario where I consider used pianos is actually very cheap pianos ready for rebuilding. You spend about $1,000 in the rough piano and spend the rest of your budget in rebuilding. You would need a piano worth the effort (Mason A, AA and BB usually great choices, although hard to find a rough one for rebuilding under $5,000). Knabe, Chickering also good choices. I have heard Kawais KG-5 have a lot of potential too (make sure is an old one, the rim made of oak). Don't pay for the cosmetic stuff, spend all your money in belly work (hammers, action, restringing, pinblock, soundboard and the rim).
You can save some money if you expand your search to Chinese pianos.
There, I have posted and did not disect the Steinway. Don't tempt me, though.