IMHO, unless you're willing to setup a regular business payment should be calculated in liquid measurement.
Two challenges with charging for work in a home shop:
1. Liability: In the unfortunate event that something you did causes bodily or monetary harm you can find yourself in a heap of trouble. Your homeowners insurance won't cover business liability, and the lawyers will go after anything you own including your home, with the shop & tools. Don't think that only working for folks you know will protect you, if they get hurt their insurance company will be the ones coming after you regardless of if they want it or not.
2. Competition: Many places don't have any independent shops left, or the ones that exist don't want to take in small jobs that don't pay much. But.... The fact that you're operating out of your house, without employees, insurance, taxes, etc. gives you an unfair advantage. It only takes one would be competitor to turn you in to the local zoning authorities or business licensing department to also make your life more difficult than you would wish.
I know there's plenty of folks who do small jobs without any problems so it's not necessary to tell me how I'm chicken little with the sky falling. Do as you will, but I've run several small businesses and decided how to charge based on overhead, expenses and profit needed.
If you're using up tooling have your buddy replace it rather than charging if you can.
Also, $60/hr is too low....
John