i agree that Craigslist is a very good option. also Facebook groups/marketplace is another good one. Kingsnake, Fauna, etc. are not the best IMO b/c unless the cages can get flat packed and shipped, most are local sales b/c shipping is usually too expensive.

lastly reptile expos are good alternatives. i often see used Vision cages, acrylic cages and sometimes nice PVC ones available. there's also usually someone selling $5-$10 used glass tanks and terrariums at my local show.

keep your eyes open and good luck.