I currently have an exhibition running of 40 prints from various gigs and concerts going back over the last 7 years. Never been hassled and many artists have contacted me for permission to use their photos. Never been asked to cease and desist or remotely threatened with legal action. My approach would be, well, if you want to cover my production costs I'll remove the image. That would total about $5,000 per image in time, energy and materials. Or you can just pay me the $600 asking price and take it away for yourself! Again, important always to distinguish between a "fine art artefact" and commercial use of the image to promote or sell something else. There's an enormous difference.