I would suggest looking around at other shops/techs and seeing what the going rate is.
I'm probably going to end up using something similar to this.I hadn't thought of a payment like that newbie, that is a really good idea.
Do a base rate for simple things, and if something is going to be more involved it will cost more.
Basic maintenance $20
External Gearbox repairs $15
Internal Gearbox repairs $25
Re-wiring of gearbox $20
With deans +$5
External upgrades $20
Custom work will be discussed and can figure a price out on a case by case basis.