here are some affordable but good psu
-coolermaster gx 650w
-silverstone strider plus 500w
but my favorite is an fsp everest 600w/800w, affordable and great psu.
None of those units are what i would call affordable.
The CM GX650W is a terrible unit btw and is overpriced.
The Strider is good but expensive for a 500W unit.
The FSP is well over $100.