Thanks for the replies, everybody. Part of the reason I was going to do the buy/sell thing was that I have a stepson who will be playing high school basketball this year, and that seemed like a decent lens for that purpose. So, it's still up in the air, but I'm leaning toward renting for now.
If you use lensrentals.com, they will give you a coupon worth a minimum rental fee discount if you buy the lens from their recommended dealer.
I really like my 135mmL, and use it whenever I can, but sometimes, its just not the right focal length.