Some of the advice you have been given appears to be inaccurate.
The Tom's chart showing 307W for a single GTX 460 under full graphics load is reporting the TOTAL system wattage drawn AT THE WALL. At 90% efficiency, the actual wattage THAT psu actually used to drive the whole computer was ~275W.
So if you believe your psu can deliver close to the numbers it tries to report on its label, you would be fine.
OTOH, a $26 600W psu with at least one math error on its label is something to be skeptical about
Here's a powerful enough psu for $40 after MIR:http://www.newegg.com/Product/Product.aspx?Item=N82E16817341012&cm_re=ocz_stealthxstream-_-17-341-012-_-Product]
that got a pretty good review from a respected source:http://www.hardwaresecrets.com/article/OCZ-StealthXStream-500-W-Power-Supply-Review/798/9]
When you read the review you will find other recommendations you may want to check out.