Any cheap but good speakers with bass?

Under $500 is pretty tough. The only speaker I would recommend is the Infinity SM-??? I think its the SM-150, with a 12 or 15" woofer, mid and tweeter, and its like 93-95 db efficient. These cost more than $500 through ripoff sources like Crutchfield, but they are available for under 500 a pair elsewhere, if you look (like 50% of what they are from crutchfield). One of my friends got a pair a couple of years ago and they play incredibly LOUD with lots of bass. I think he got them through a visa-type buying service but the only place I have seen them recently is crutchfield. You will know these by the foam tweeters. For the money I would get these if you want volume and bass but look for a price at about 50% of retail because they are not part of the mainstrame marketing by Infinity.

Used AR 303

Have you considered adding a small sub woofer? If so give me a buzz. I have a velodyne ct 100 I am offing. Plenty of punch to back a couple small speakers. This is just a suggestion not a sales pitch. Any sub would do the trick.