You should be able to get a pretty good set of speakers for $400. You can go with the Pioneer setup of: SP-FS52, SP-BS22-LR, SP-C22 and get a sub when you can. I know it's a bit out of your budget, and I hate being one of those people to suggest things out of a person's budget, but these speakers are easily the best bang for your buck at the moment.
I started off with the SP-FS51's in a stereo setup and had problem waiting to get the rest of my system. They sound great and can easily play down to about 45Hz, which will help hold you over until you can pick up a sub.
Now, I have the first gen set of these Pioneer speakers, and the ones I'm suggesting to you are the second gen set. If you could find the first gen you would be able to get it for under $400 most likely, and still have a great setup. Best Buy still seems to have the first gen in stock.