I'd like to get involved in painting houses. How do I figure how much to charge

I have always used a formula that's basically this-- figure out how much the materials you need cost then multiply that by 5 to get the cost of your labor. This is also known as return to labor and management in case you decide to get someone else to help or you use materials like brushes and scaffold and ladders that you already own.

My father does custom machining and usually contracts his labor as 2x material cost. It's a rough-and-dirty estimate. If you are fast and good, then you can price lower than if you take a while and pay particular attention to detail. Depends on who your clients are and what they expect.

Any good tradesman is worth his weight in gold. Most people don't want to get their hands dirty! You can always start high, charge what the traffic will bear and drop down if you need to. It's harder to start low and then raise prices especially with existing customers. Or you can meet with the client and tell him your normal rate, then if you meet with price resistance you tell him you are running a special or that his job can be discounted for some reason. It's like going to an auction. You have to market your services.