Actually I've recently started giving my fees in "hours" rather than "nights" because I needed to find ways to make my fees a little more fair for myself and my employers. In addition to playing time, I now charge for "cartage" (setup/takedown time - got this from the Musicians Union which allows cartage fees for players with excessive equipment). Some places I play supply a good piano so I do not charge them for cartage. But most of my gigs require that I use my gear and that costs time and money for me so now the cost is recoverable, and can be negotiable. For example: gigs where I provide my own equipment, I wave the cartage if they hire me for more than one consecutive night and I can leave my gear set up. This dissuades clubs from hiring me for say Tues/Thurs/Sat which would mean about three hours more cartage work for me than if I played Thur/Fri/Sat. I've actually have gigs bump their other performers to take advantage of this because the other players charge the same regardless! I typically charge regular/club engagements around $50/hour and private parties go for twice that, plus cartage takes an hour. So a n average four-hour one night club gig would go for around $250 but two nights would go for $400. My minimum gig is two hours plus cartage ($150). I no longer work with singers so that's my fee as a soloist. I've also set $50/hour as my consulting fee if I have to do extra work to prepare for a gig, such as learning special music for weddings.

The MOST important thing with pricing is consistancy because your employers will talk to each other and compare notes. Also you have to be competitive within your market and charge accordingly - but even there you can do better if you can outclass your competition while offering fair deals to your employers.