I sold a framed SuperA3 print of my Rhosydd photo (the one I won the photo comp with) in a local art gallery for £250, but that was with 40% commission for the gallery, hence the hiked price! I was as gobsmacked that they'd sold it as they were though - it was just an experiment to see if anyone would bite. Apparently it was a posh middle-aged lady who bought, it who thought it 'exciting and beautiful'. So there you go.
The Thornhill lead-mining book I worked on with Jim Rieuwerts (I did the underground photography and cover design) has just about sold out as a limited edition of 300 - at £25 for luxury hardback it was a bargain, but then we didn't pay for production, and I think 300 was probably just about right given the target market. But quite a few people I know bought one because it looked good, rather than a sudden interest in lead-mining!
So I think money can be made occasionally from this game, but I also agree with the above - unless you've got an agent, sponsorship and the biggest and bestest caves in the world to visit like Shoney has (for public appeal/sub-editor interest), it's not going to produce a living, that's for sure.