I'm not clear about whether you already have the Antec PP303X power supply, or are planning on getting one to install.
If you don't have the p/s yet, then just buy the Antec KS282 or SX830 both of which come with the PP303X.
KS282 is slightly smaller than the SX830 and has fewer bays (I have the KS282 because I don't need the extra bays).
Bought mine from
MyChaseShop. Last time I checked the KS282 with the PP303X was about $58-60 shipped, the SX830 about $68-70 shipped. Price varies since you get free shipping if you register (shipping is only $3.50 per order), and can take a 5% discount if you use a Chase Bank card.
Site listings are not in best format, but not hard to figure out. Just do a search for either one.
Prices are actually a little better than even Onvia's.
Reviews:
KS282
SX830