Example 1: Your four-piece bar band Will Play For Beer makes about $50 per player, so one gig during the year everyone makes $40, including WheresTheGig.com. (Doing the math, this comes to $10 per person for the year, or about 83 cents a month. Quite affordable!).
Example 2: Your eight-piece showband Big Bucks Review plays events for such party-animal groups as "Amalgamated Actuaries of America" and pulls in $12,000 per gig. It costs a lot to run a show-band, but even after operating expenses players typically walk away with $1100. So one gig during the year everyone makes about $980, including WheresTheGig.com (and everyone enjoys how fast the site goes since I can afford my own co-located server :-).
Your band probably falls somewhere between the two (and more towards the bar band
example). Donate what you can. Thanks!