Need Plate Amp for small sun enclosure

You can look at a plate amp or a standalone amp at Parts Express. The standalone amp could run ~$200.

You can consider the BIC PL-200 12" subwoofer at <$300 that is highly recommended in this forum.

If you have an old receiver/amp sitting around, you can have you AVR output LFE (sub out) frequencies below a certain point. Plug the rca cable from the sub out into the receiver amp and use one channel of the second amp to drive (via speaker connections) you dual 8" subwoofer. I used this solution quite a few years ago when my second standalone subwoofer amp blew (at the three month mark). I later discovered the the company making the subwoofer amp had gone out of business.