IMHO, I haven't seen the selvage ever fray. You don't HAVE to hem it, though it will likely last longer. (see Below)
You indicated that you have 15yds of material, but a 10' or 11' hammock isn't THAT big. You can try your local cleaners and alterations shop. I'd bet they'd do it for $10.
If not, and you still want it hemmed, check the local sewing shop... Somebody will do piece work... Hemming isn't that hard.