First, I'd consider some different subs. Unfortunatley, you're not going to hit "really hard" in a Miata, not only because it's a convertible....but space is so limited. Putting subs in your trunk probably isn't going to do a whole lot other than rattle it. In most higher end convertibles we work on, we do a JL 8" woofer (custom fiberglass enclosure and completely stealth) on the floor under the dash of the passenger side, still allowing enough leg room for a passenger. It's the best way to get clean bass , but is not going to be "glass shattering." If you're willing to lose more leg room, we could squeeze a 10" woofer in there. Either option would run right in your budget range. Otherwise, we could definetly do an enclsoure in your trunk for the 2 12's...but I wouldn't exactly recommend it. Come by SoundAdvice on Columbus and Dale Mabry and one of the salesman would be happy to go over a couple options with you.