Alot goes into determining the rate of charge for work. The demographic of your area and the specific nature of your work will vary the amount greatly. When I first obtained my contractors license, I was charging about $10 below the local average per hour. This ended up hurting me more than it drew in customers. People assumed my work would be cheaper, or that I was not as qualified as the other guys. I soon raised my rate to everyone elses. If you plan on doing a per unit rate, you must figue in costs, overhead, labor, and profit to come up with a good number for each type of installation. The best advice: just becasue you are new doesn't mean you have to work at a loss. Don't be afraid to charge what your service is worth.
Remember this what you charge can make ya or break ya. if you go to far over at first you will drive customers to go else where, if you charge to little either you will be looked at like what's wrong with your work or you wont beable to cover you expence and have allot of cost over runs which will cost you. this has to be wheighed out and even requires a little dectetive work.