i would invest all that $450 into a downpayment on a decent Onkyo receiver. when i purchased my receiver when i worked at best buy about 4 years ago, i picked up the best receiver the store carried at the time. it was a yamaha, and i don't remember the model #, but it was $800 before discount.
you are going to have to spend atleast $500 on a decent receiver. like these other guys said, its the core of your system. you don't want to go low balling on it. good speakers won't sound good without a good receiver.
home audio stuff is not somethign you buy all at once, its stuff you buy in pieces once you have enough saved to get each part. i would NEVER EVER EVER EVER get a boxed 5.1 set that is like $500 or so. that basically looks like what you are trying to do. unless you want to upgrade in a few years or so, i would suggest buying in pieces until you can afford stuff that is actually worth while.