Here is a website you can check out-
www.southernpetsitters.com
The owner is fantastic and does enough business to have several pet sitters.
Shes got her prices listed on the site. Depending on where you live, you may even be able to charge more. If you have a Small Business Development Center in your area they are always willing to help start out a business and can give you plenty of advice!
I have never left my older dog overnight except for her spay and once I left her with my mom when I was moving and the new pup hasn't been left at all, so we havent' used the service much, but I did take my girl to the beach one time and had the service come and walk, feed, etc the foster puppy I had at the time. It was great and well worth the $12 for each visit. They even worked on her commands while we were gone so she wouldn' forget them. A big thing the do is write cute little notes and leave them at the end of each visit so when i got back I could she what marley did and how much she enjoyed the pet sitter!