i charge $20 an hour for sewing for people. but in this case you really should have discussed a price before ever taking it on. for good friends i have done repair work and finished things for flat rates..."oh, sure i can do that for you for about $25...or i could do that but it would probably cost about $100, do you really want to go that route?" it really depends on the project; time involved; who i am doing it for, how extensive the repair work is...
your time is valuable, if you are going to sew for others you need to take the time to decide just how much your time is worth to you, how quickly you sew, your expected expenses (you need to remember, thread costs money, and wear and tear on your machine...don't short change yourself. (and that does not mean i do not sew for free plenty! i have a big family...but every once in awhile i refuse to do a sewing job even for family without being paid for it.