I have been a longarm quilter for seven yrs. I charge by the sq. inch. My prices vary according to what my client wants done on his/her quilt. Basically a loose meander would be $.01 per sq inch. Price would rise accordingly if more dense quilting is desired. Prices for pantograph work also varies according to density and complexity. Panto prices start @ $.0125 per, sq. inch. Custom work also is priced according to density and complexity of design. In general I typically charge $.03 - $.04 for dense custom quilting.
I personally don't know of any quilters in my area that charge by the hour though there may well be some that do.
On occasion I have rented time on my Gammill for people to quilt their own quilt but honestly don't have that many clients that wish to do that. I don't have a second machine or room to add one so don't picture myself doing a lot of renting.
Another thing I do on occasion is to barter for services with a client. It's a win win situation for both myself and the client.