I have a few blocks away who lets people use her Gammill for 1 cent per square inch. She does the set up and provides the thread, I think. I haven't tried it yet, but would definitely do so before I consider buying a machine of my own. I could do a lot of quilts on her machine at this price without spending nearly as much as the cost of a longarm, and I wouldn't have to deal with the loss of space in the house or maintenance costs, etc.. This person in the area has two longarms in her house and it's an official business arrangement. She most likely has insurance, but I didn't ask her about that. I found out about her merely by chance because we were shopping for fabric at the same time and started a conversation about what would go with what.
I don't yet know if she has some requirements about the renter having basic instruction (and paying her for the time that would take). There is a company some distance across town from us that rents the use of their machines for a similar price, as I recall, and they definitely require you to take a class from them first. You provide the materials. I don't remember what the fee was. This was a few years ago, a dealer I talked to at a quilt show. I didn't do it mainly because of the driving distance. Worse than that, I've lost their business card and don't remember the name.
If you are in a guild, you could poll the other members to see whether they'd be interested. I would think there would be many who would love the idea. If there is enough demand for this it is not an insurmountable problem to get a business license and appropriate insurance. Running a business could be a whole new "hobby", however.
One other issue that might come up would be deed restrictions. Many neighborhoods do not allow people to run businesses from their homes. One like this would have very low impact on the neighborhood because you'd only have one person at a time visiting, but if they enforce these restrictions they have to enforce them across the board. It's very interesting to pull up Google Maps and see the names of businesses that often pop up in residential neighborhoods where I'm pretty sure they are not allowed. In some cases, a variance can be granted, but you should go through proper channels to make sure they don't throw a monkey wrench into something after you've put a lot of work into it.