Ya, rly.
And $25 an hour? No way.
4 hours - Playing time. Say it's a 9pm-1am since OP said it's 4 sets.
+ 1 hour - Get to the gig at least an hour before for setup and sound check.
+ 15 minutes - What a very quick tear down and load into the car would be
+ 1 hour - Travel time, round trip. I very rarely get to drive less than half an hour to whatever venue I'm playing.
So about 15.25 an hour. Then the tax man is going to take on top of that. AND you haven't factored in gas as well as possible food/drinks.
Well, after reading through this thread, including the posts after this one which are responding to it, I agree with you. First of all, to those who say normal jobs don't pay you for gas, travel time, etc.., that is irrelevant. As a sub you are basically a contractor and all those expenses absolutely have to be factored in. The trade off for normal jobs not covering that stuff is, and always has been, guaranteed 40 hrs a week, benefits, etc. As you are basically running a business which you are responsible for the tax liability of, those expenses should NOT come out of your bottom line.
Also, since I have never subbed nor given the issue any thought until now, I would suggest that your estimates concerning your time spent on the gig are actually low, based on several factors pointed out in this thread which I previously hadn't considered.
So yeah, unless these are friends of mine or someone with which I expect to gain something from in the future, $100 is not enough to even consider. $200 may even be a stretch.