I have a custom made single sealed enclosure, for a 15" sub. Its about 3 cubic feet, and is fully carpeted in grey. 3/4" MDF construction, fully silicone caulked, terminal cup. Literally all you would need to do is drop in (the sub) and and screw it down. I'll even throw in any wiring you might need. Very well built by a local shop (Had to buy one, before I bought wordworking tools!).
I had a 15" Brahma in it, and it absolutely slammed with about 2000w. I know you want a ported enclosure, but hey, this is cheap.
You can have it for $25.00, I paid $50.00 for it. Just come pick it up!
I'm in LA County area, Santa Clarita.
Hit me up on PM if you are interested. I have pics.