Renting sound like a good idea if there isn't more work to do with it.
I was thinking of buying one but not sure when, where or which one, looking at the eta Unit for a Compact Tractor.
Just a comment, I have never used one but all of the videos I have seen on the subject suggest to dig a foot and pull it out, start again. That was going to be my method when and if... luckily I don't have a lot of tree roots, just rocks.
Good luck and post what and how you make out.