Im afraid at that budget level, you're going to be restricted to the small HTIB setups that offer little ummmph. To purchase a complete 5.1 surround setup that can crank, you'll need to add a bit more $$$ to your budget. You might consider starting with a two channel setup, and working your way into 5.1.
You could start with a receiver $350, and a pair of fronts $450 to get the ball rolling. When you save up more, you can add a center speaker, then surrounds, then finally the subwoofer. At least then you can crank some 2 channel, and you can use your center, surrounds, sub from your current HTIB setup to run off your new receiver as a band-aid for movies until you can make more upgrades.
Since you asked, I'll give you an example of what I'd call a 'good start' to a budget system......
Pioneer vsx-1015 $370
http://www.compuplus.com/i-Pioneer-VSX-1015TX-71-Channel-AV-Receiver-with-THX-Select-2-Certification-1005623~refer-pricegrabber.com.html
This is a quality entry level receiver that has a lot of options, and room for expanding your system
These are towers that can crank and sound good on a budget, I'd recommend Klipsch because they offer a big bang for the $$$
http://www.klipsch.com/product/product.aspx?cid=981
These little guys can pump out good sound for a very modest price. Expect to pay about $450/pr. It you want to rock, there is no substitute for tower speakers because they can reproduce a wider frequency range, will have a fuller sound, and provide more kick compared to little shelf speakers. I highly recommend the reference line over the Synergy that's sold at Best Buy.
That would be my interpretation of a great start to a budget system, but you'll want to save your pennies for a little longer because you'll need about $800 to get the ball rolling.
Anyway.... that's my 2 cents.
