I don't know alot of things - I don't think that there would be a software 'package' that you can use for such a purpose. I used to run a dealer workshop & I would often get calls from other dealer workshop managers who would be checking our rates so they could keep theirs similar. You may have to make some calls & find out what local dealers & repairers are charging. It would also depend on the area where you intend to work, the setup & equipment & tools you have & knowledge / experience you have to offer the customer you were looking for - owner operator; fleet owner; mining contractors etc.
My rates are about 20% lower than the local dealer & that is barely enough...........alot of expenses - insurance; superanuation; vehicle running costs; tooling; manuals; workers compensation; & of course....TAX!
You may have to start on a lower rate just to get people to give you a go.
Don't want to put you off but research, research, research.......
If all else fails - try it & see how you go
Good Luck ! :drinkup :drinkup
PS - (other expense - alchohol to ease the stress)