One thing I learned about running a business is "Sell on price, lose on price". You don't want the business from the people that are worried about price. You want the business of the people that want the job done correctly. Period....End of discussion.
Also, learn from my mistakes. $40/hour is NOT worth getting out of bed for if you ask me. To someone that's making $12-$15 an hour, $40 sounds like a lot, but it is not.
You're going to be traveling, so there is wear and tear on your car. You'll need insurance in case you drop a screw driver on their dog, they sue you and try and take your house. You'll also be paying both sides of the taxes when you file, which they call the "Self-Employment Tax". I could go on and on.
Look at it this way, if you do a 1h job with 15 minutes of travel on both sides, you're making ~$27/hr. Subtract $3-$5 for fuel and you're down to $24. Wear and tear on the car another few dollars. Pay the taxes on that and you'll be lucky if you hit that $12-$15/hr I mentioned above. Oh, and you'll still have to deal with the phone calls, the emails, the call backs, going back because you don't have a part, people that don't pay, etc, etc.
I'm not trying to dissuade you from starting a business at all. I'm just trying to keep you from making the mistakes I made when I started. If you're good at what you do, you need to charge more....A lot more.