So what's the conclusion?
I have precisely $100 to spend, no more no less (well, if you don't count shipping into it). I'm trying to squeeze the best performance into my system with such "small" budget.
well there are a few options:
1) get the 650 w/o getting another PSU and see if it works. if it doesn't, your PSU will fail and you may take out the whole rig with it.
2) get the CX430 for $39.99 then use the $20 rebate when/if you get it to buy the 650 for $79.99 and stay in the budget.
3) beg/borrow find somehow to get another $20 to buy everything for $120
4) or get a 7750 for $89.99
PowerColor AX7750 1GBK3-H Radeon HD 7750 1GB $89.99
it uses ~20 watts less and will work with your PSU and equal to a 650's performance.
i wish i could give you the best answer out of those, but that is up to you.