To set your standard hourly labor rate look to get about 4 times what you are paying your tech or at least 2.5 times your fully burdened rate. If my tech was traveling multiple states I might want to have full day or one half day minimum billing increments. I have used $230 for per diem which includes lodging and meals. Only you know what your service vehicles are costing you (capitol cost, maintenance, fuel, insurance, etc...) so you might want to add a suitible mileage charge.