So a quick look shows the 3.5/square inch price which for them includes the batting. There are additional services for reasonable prices. I think with the turnaround etc.and the security of dealing with them in particular, it all sounds pretty reasonable. But add shipping costs!
I have ok skills and have been working on improving my equipment to do this level of quilting, but a queen sized quilt still takes its toll on me physically. I was just about to start quilting down a project this weekend but my machine decided it would rather go to the shop. I had access to a friend's long arm for a number of years and got spoiled, I have the skills to do what I want on a long arm -- which still has quite a bit of physicality, it's just different. You might look at renting long arms as an option that brings down the cost because you are providing the labor, but they are providing the machine.
When I price out my tops for what I want done, here in the Seattle area, it would be about $350-500.