i hope the powersupply you have is good enough. but there's nothing power hungry here, so until you add a video card (which you won't need to unless your 12yr old decides to play Doom3 or something..), the 300watt should suffice. you can stick in your optical and floppy drives in there. and you also have to add taxes and shipping which i didn't.. so you'll go a bit over $400.
if you have to buy anything else, then you'll have to downgrade to socket 754 to stay within budget...
"Is virtue a thing remote? I wish to be virtuous, and lo! Virtue is at hand." -Confucius