Well I can't recommend one supplier over another, because I'm only familiar with my local suppliers here in Australia. But it seems to me that if you purchase the components from there, then this does not add too much to the purchase price:

http://www.newegg.com/app/viewproduc...102-151&DEPA=6



I'd also change from an Athlon XP processor and motherboard. Athlon64 Socket 754 alternatives are not only cheaper, but they are also a better performance alternative.
http://www.newegg.com/app/viewproduc...180-061&DEPA=1

http://www.newegg.com/app/ViewProduc...103-486&depa=1


The other suggested components would be compatible with those.

I have seen decent barebones systems for $200 ...
Check out pricewatch.com