Search ebay. I've seen them on "Bid and Buy" auctions for $93 + $17 shipping. That's about as cheap as you're gonna get.
If you're gonna run just one, I'd suggest a JBL 600.1. Two would of course require a 1200.1. For SPL run them in a large ported box (2.5-5.0 cubic feet each) or for a mix of spl and SQ i'd go with a 1.25-1.5 cubic foot sealed box. A smaller sealed box is slightly louder, but the larger box gives the low notes a real kick!
Have a look at my signature......should give you an idea of what these subs are capable of //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
ikesound.com has them for 110 they don't list the price but if you call they will give it to you whan I called a couple weeks ago it was 110 hope that helps