@Tinkyandi far too cheap. Although it used to take me about 20 mins, i could spend 10 mins unpicking original hem and tacking new one up. I always used to tack as they are sewn from the right side i needed to make sure i had every thing tucked in. I charged £8, apart from the chap who spent £350 on his jeans and then i charged him £15 (my reckoning was that he could afford it).
Bear in mind it is 5 years since i stopped "sewing for others" so would probably charge more now.
It may seem like a good hourly rate but take into consideration the wear and tear on your machine, cost of running your business, even if you are based at home you are still paying for electricity and heating, insurance, both public liability and your house insurance plus increase in Council Tax if your business is home based and paying for supplies including postage cost and your profit soon dwindles.