Well you will have to expand your budget, any low profile GPU demands at least a 300W PSU so you also have to invest on that.
Currently there's a sale on newegg for a R7 250x, you should take advantage of it while it lasts (70$):
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150716&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-PCPartPicker,%20LLC-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=
But as I said above, you'll also need to upgrade your PSU, this EVGA 500B will do (45$):
http://www.newegg.com/Product/Product.aspx?Item=N82E16817438012&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-PCPartPicker,%20LLC-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=
You could go with a cheaper Antec VP 450w if you don't plan to...