The Audioholics store has Infinity Primus P162's for $85 per speaker with free shipping. That is a very good speaker also. The Primus p152 is on sale at $75 each, that would be good too. There is also the Behringer 2031p, your onkyo could drive that, and it has more powerful bass then the 2030p. I think these are the best deals in inexpensive speakers, its hard to do better than them for the money.
For a sub that could hang with a system like that, look at the Emotiva Ultra Sub 10, which is on sale right now for less than 300 shipped. There is also the Hsu Research STF1 which is a tad over 300 shipped. Both of those look like they have pretty high quality bass, especially for the price.