If you want to get two for under $200.00 I like JBL's. I personally feel that they reproduce bass nicely, model GT100. I also like Alpine type R 10 inch sub, they are built pretty tough and you could get two of those for around $200.00. My brother has two rockford fosgate 10's that have lasted for quite a while now, but I personally don't like their sound.
could get a couple pioneer premier 12's or a 12 L7. both would be good. i would take the premiers. since u only want one sub the L7 is 200 bucks, but how much power did u want to have?