Here is a list of energy efficient PSUs between 400 and 500 watts and under $75. Newegg.com - Computer Hardware,Computer Cases,Power Supplies,$50 - $75,80 PLUS Certified,401 - 500W
That's plenty for your system. Your video card maxes out at 57 watts (under 5 amps). The CPU is rated at 65 watts. Everything else will be considerably less.
The 1 TB drive you are getting may use no more watts than your existing drive, but minimal in any case.
Stick with a major brand:
Corsair, FSP, Seasonic. maybe OCZ.
Off that list, I would go with the $64.99 Corsair. If you get the rebate, it's $10 less than that.
Don't agonize over the additional details. Just make sure it will fit into your case and has the appropriate number of connectors.
You have a low to midrange system, so any PSU should have enough connectors. You may want to consider a modular PSU to minimize clutter---you can disconnect the unused cables.