If you register with RR Auction, you can do a search of past auctions and get a good idea of what they've sold for in the past...at least with regards to that auction house. A quick search over the past 12 months shows that they typically sell in the $1000-$4000 range...with higher money going towards nicer quality examples, examples with solid provenance, and/or examples on more desirable photos. One very nice photo, signed to Irving Berlin, with solid provenance, sold in excess of $20,000.