It looks like the subwoofer to aim at with this budget is the BIC F12? ($184.31)
Is the Jamo set better than those Polk speakers? I added a pair of Polk Audio Monitor30 Bookshelf speakers for surrounds, and the total came out to $415.94 for the 5 speakers, which edges out the Jamo speakers on price slightly (for black finishes). However they're the same general setup, so I don't know if they're very similar, or what.
I guess for reference, here's the list as I've currently got it estimated:
Part Price Qty Subtotal
Onkyo TX-NR609 $399.99 1 $399.99
BIC America F12 $184.31 1 $184.31
Polk Audio Monitor M30 Bookshelf $89.99 1 $89.99
Polk Audio Monitor M60 Floor $109.99 2 $219.98
Polk CS2 Series 2 Center $99.99 1 $99.99
Which totals $994.26.