MegaFit isn’t too far from Jinjiang I believe, plus it’s possibly the best gym around in Chengdu. It’s probably around 2000rmb/year or slightly less, unless you wait for one of their promotions. If I remember correctly they gave out 1000rmb/year subscriptions about a year ago.
Check out Working out in Chengdu
Plus some more info about gyms in Chengdu in this thread:Girly man gym