The wattage that a PSU is rated is how much it CAN provide, not how much it WILL provide. So if you have a setup that uses 300W, the 650W PSU will give you 300W. You can go over as far as you like because the PSU only supplies what is needed.
As for the 650W for $30, I'd be careful. What brand is it? Post a link for us to check out. Cheap power supplies are typically pretty crappy.
do you think 400 watts will be good enough to run a
amd 64 3500+
256 meg vid card
(1) sata 150 hard drive (300-320 gig)
2 floppy drives
1 cd drive
1 cd rewritable drive
is estar or echo star a brand name psu or are they generic