Researching a painintings value/price

Are there any useful free resources on the net for researching past auction prices of a painters work?

I don’t know about free and on the net (too busy to check today) but there are a couple of auction catalog databases that if you at least have a uni library account you’d maybe have access to-- SCIPIO, and the Getty Provenance Index (I think the latter is probably accessible-- they’re generally cool about access)