HD5870 at 354$
http://www.newegg.com/Product/Produc...-329-_-Product
GTX470 at 280$
http://www.newegg.com/Product/Produc...-110-_-Product
HD5850 at 259$
http://www.newegg.com/Product/Produc...-318-_-Product
GTX460 at 220$
http://www.newegg.com/Product/Produc...-115-_-Product
My suggestion: if he needs that computer before october sometime, get him the HD5870 or the GTX470 for nice performance.
The pros of HD5870 are less power and heat and also less noise and highest performance of the cards ive listed.
GTX470 is up there in the top, but all the pros are now negatives. Heat, noise and power used are above the HD5870, but its still not a bad card, especially at that price, it really depends on what kind of noise/heat etc you can "live" with.
HD5850 is hard to really recommend since AMD doesnt drop the price on it. It has been the best performance/price card since it got released but atm that title should be rightly given to the GTX460
GTX460, especially if you go for the 1gb versions with overclocks straight from the factories, like the Gigabyte one at 810mhz core (price is 254$, same as the HD5850) or the Gainward GLH at 800mhz core, is a very nice card and definetly the best price for performance card out there now.
If he can wait a few months (no official release date), AMD is rumored to release their next series of cards, which should drop both the current card prices and likely introduce higher performing parts.
GL