I charge $20 an hour to clean houses, so if you paid a sitter $7, you would still be ahead of the game. I don't see why you couldn't clean on weekends, but ideally I would try to get 2-3 houses on one day a week and pay a sitter for that day.
The other thing I do is clean new construction. This is what I prefer as the money is better and the houses are empty of furniture. I charge $0.15 cents a sq foot and extra for windows that need a ladder for cleaning. Of course with the housing market I haven't had a house to clean in ages. The only thing with this is you would need to get a business license and tax ID #. I think I ended up paying a total for @ $100 for license, tax ID and registering with the state.
I forgot @ most people's books being computerized now a days. If you had a program such as quick books or peachtree, could you still do it from home? What about with remote log in? Go in the evenings and do their books?