What is your target pest on River Birch? on Maple?
These are trees that dont routinely need to be treated.
Also, what good could you possible be able to do with one broad spectrum application per year and who advised you of this?
I dont think you are going to get much more help on pricing as different products have different pricing.
If you have been using an IPM program for years and have not incorporated soil or tree injections as part of your service, you may not be using an IPM program.
As was said in another post, mauget and like products are a specialty product, not one that is used as a replacement for say...an oil spray.
It does sound like you just may be a touch out of your league or at the very least out of your area of expertise with this project.