Try the JBL e150 (10" and 150 wpc) or JBL e250 (12" and 250wpc).
I got my e150 for about $165 shipped, new, from eBay. In retrospect I would now spend the extra $50-80 for the e250 since my living room is cavernous, but for a smaller room the e150 should do just fine, esp. for HT.
For the money, I'd try the Dayton 10". I was in your same situation 2 months ago, and I narrowed my search to the Dayton and the Atlantic Technology T70.1 PBM. As far as I know, these are the only two that can reach 25Hz for less than $200. I went with the Atlantic Technology for aesthetic reasons, the video shielding, and the sealed design (better for music IMO). I'm quite happy with it and I have tested it to 25Hz. It fills my HT room which is 18x13x8ft with ease (set at about 33% volume). So why do I recommend the Dayton? It should be about $50 cheaper with similar if not better performance for HT use. But either one would serve as a good stepping stone. For more info on the T70.1 PBM go to soundandvisionmag.com and do a search. Good luck.