A used Model 29 Smith & Wesson will be around $400. This unaltered and with factory stocks. Add more if pinned barrel and recessed cylinder. Detract if worn places in the blue, such as near the muzzle, etc. If scratched or dinged, price goes even lower.
I bought a Model 29, 6" with presentation case, rosewood factory stocks, pinned barrel and recessed cylinder for $250 from an individual, but this was a bargain price.
Best bet, check local shops and compare. Set your price a little above what you'd want and be prepared to dicker.