Firstly, how much you charge depends very much on your experience, level, how good a job you actually do, and where your business is located (home, salon or mobile or renting space).
You need to look at your overheads (cost of products, rent, electricity, phone etc.), and work out our much you need to be making per hour to cover your costs ... time your manicure service and charge accordingly.
It of course is also helpful to know what others in your area are charging for the same service and reach some sort of a compromise.
A lot of manicurists around my area charge anything from £12.00 onwards, i am mobile and have priced mine at £12.00 i only do a basic manicure but you can get luxury manicures and i know they can be a mit more expensive but as gigi says it does depend on a number of things. Hope this helps anyhow x x