AMD's offering is the r7 250 for ~$74 on newegg;
http://www.newegg.com/Product/Product.aspx?Item=N82E16814125829&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-PCPartPicker,%20LLC-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=
Nvidia has the GT740 if you prefer the green team;
http://www.amazon.com/dp/B00LCADCT8/?tag=pcpapi-20
I believe they are approximately equally levelled cards performance wise, so take your pick
Twig ~
EDIT: You'll find that as your brother mainly plays games which are CPU bound, upgrading the GPU won't affect the frames so much, the 5850 he currently has should be fine as what I have aforementioned aren't great/worthwhile upgrades for the budget allocated.