no don' get an 18, if you're looking for a little bass like you said, get a couple of nice 10's or maybe a 12, that should work well with your 200 watt amp.
I had a memphis 12" HPO going off of around 300 watts in a 2.0 cube at 32 hertz box and it wasnt to bad. most people couldnt belive it was that low of wattage.