Last time I checked, which was a while back, about 1.5 to 2 cents per square inch was fairly standard for light pantograms, edge to edge. The price goes up for custom quilting.
I bought my longarm only a few years after I started quilting, because I wanted to finish my quilts myself and was tired of either quilting in sections or stuffing 8 miles of quilt through a tiny throat. I had the money and the space and was making 10 or more quilts a year. Even after the expense of having my machine upgraded a couple of years ago, I do think it has paid for itself. I think without it I would probably have a large inventory of unquilted tops.
However, if you are making only one quilt a year, and your current longarm setup isn't working, it makes more financial sense to have someone else do the quilting.