The $10 - $20 between quality power supplies and everything else is that it won't degrade over time. Quality power supplies are rarely swapped out when other components are upgraded, so it is worth the $10 to $20 extra.
If you have to get something cheap, go with a EVGA 500B after that it is XFX 550, XFX 650, EVGA 750 G2, EVGA 850 G2. Past 850 Watts is Corsair AX or EVGA P2 depending upon sales, budget and preference.
That is how my list goes but I always feel uncomfortable recommending any of those specific units unless if people need a power supply unless there is a sale going on but everyone hops onto the forums 3 seconds after a sale is over to ask for power supply recommendations or comparisons.