I don't know of any longarms for rent in my area. Most of the shops don't have longarms at all, and the one that I know of that has one does not rent it out.
When I bought my longarm, however, it was from a shop that did rent time on their longarm. (It was about 6 hours away from my home, so using their longarm on a regular basis was not an option.) I learned enough in the lessons that came with the longarm that I could do a decent job on a quilt, as long as I kept it simple. But comparing their price for renting the longarm, and the time it took me to finish something, I don't think it would have been cheaper than paying a longarmer to do the same job.