Since every vehicle and its condition is different, I don't have set prices for specific services. I charge $50 an hour, and tell the customer what I can do and how long it will take by simply pointing out things on their car. This way they can decide what they want done, so ultimately the total cost is on them and not me.
One thing is important, do not undervalue your time. Once you do it cheap for someone, they (and anyone they tell) will expect it cheap and you won't be happy with that. Be firm, and make sure your own car is sparkling when they come by so they can see an example of your capabilities.