Then we also got some responses more applicable to a public venue:
From Rod Deacy:
Kinda depends what you want to do, doesn't it? If you want to sing cover songs and play bars, then you can make a lot more than singing your own songs in coffee houses.
People who book musicians fall into two categories; those that know something about music, know what they want and try to pay musicians fairly, and those that just want music because they need noise at the end of the room and have no particular preference after that. The latter category respond better to material they've heard before, preferably many times... Even after that, though, they often consider paying more than $50 -- $100 to be unacceptable -- they know that there are a ton of people out there who will play for little or nothing -- they may be crappy, but so what? There are a lot of people putting on private parties who think they should be able to get live music for nothing... Never mind the years spent learning to play an instrument, or instruments...
I played the college circuit (and other places) with my rock band for about 7 years and have run into almost every variant on getting paid nothing to lucking into a way profitable gig. Apart from street singing in Europe (mostly Paris and the south of France), which is the single most consistently profitable singing I've ever done, I've played on expensive yachts on the Mediterranean, villas in France and Spain and made substantial sums doing it, but these days I'm happy playing for tips... However, I think Todd's last breakdown was to the point -- $50 -- $100 for coffee shops, plus tips, and $100+ for bars (they make more money -- plus they used to be smoky :>) ).
As a follow-up to my previous response, I don't think how much the booking entity (person, business, etc) can pay should enter into the equation. Any fee(s) a performer charges should be well thought out, taking into consideration their (the performers) time, energy, drive time, equipment set up time, etc. In other words, what is your time worth. I know that I have different fees for different types of shows. Coffee houses I'll perform in for tips, $50, $75, or what they offer. I always ask the venue what they usually pay, before I give them my rate (their rate might be higher than mine). House concert is $100 - $200, depending on whether my show is one, or two hours. Weddings ? Well, it's been many years since someone asked me to play one, but I used to charge $100 back in the 1970's. Today's charge (solo) would be $200 ($100 additional for each additional member I'd bring in to accompany me).
If I'm trying to get 'into' a venue and they seem stand-off'ish, I'll offer to play for tips only so they can get a feel for my music. I've booked many good follow-up gigs this way.
Truth be told, I love to perform. Although at one time I didn't need my music income, it has now become part of my way to pay bills. Just the same, I'll play for free or very little just to play if no money is on the table.