However backup/DR/offsite is hard to price and be competitive. That is what we have been finding out.
What I'm learning is that people want to deal with one person/company to meet as many of their needs as possible, and parceling out your services bit by bit should be avoided altogether insofar as it is possible. BackUp/DR/Offsite is not unique, but as a part of your total server package it makes your service plan unique, and that much more valuable, and that much easier to sell. If you have trouble replicating across the WAN due to bandwidth constraints, just make sure you address their needs another way. People don't care how you do it, they just want the fastest possible recovery in the event of any sort of disaster, and they are willing to pay equally for the result rather than the methods employed.
I wouldn't even do the paperwork on a service that billed at $15 a month, much less assume any level of liability, unless I really thought I was going to make something big on the back end.
Marty you can just take this for what it's worth, but I think you should be trying to figure out how to up your monthly and forget about charging for the onsite visits. Creating the larger revenue streams will add much value to your business, whereas a client who may or may not call you at some point will not.