http://www.flatrateystems.com has everything you need to know about flat rate pricing.
I purchased their software called Flat Rate plus some time ago and my profits have skyrocketed!
The price may seem a bit high at first glance, but your profit increase will pay for the software 10-fold.
I’d definitely recommend checking out the site above, they have everything you need, and the best part is the owner is an actual tech who had his own service company at one point, you really can’t beat that for your flat rate pricing software.
They even offer four different industries: Plumbing, HVAC, Appliances, and Electrical. Just awesome!