I might suggest you also contact your competitors and ask them what their standard billing rates are for various services - repair, PM service. And ask what their shop supply charges, oil disposal fees, etc. are as well as service call policies are (port to port, actual or flat charge - like 2 hours minimum, etc.

What your local competitors do makes a big difference in what you are able to charge. Of course you also need to make the % margin as previoulsy mention.

You might be surprised how many will cooperate if you play "show me yours & I'll show you mine". Done it sereval time in my career