Budget GPU?

[mein]

Looking to get a gpu for anywhere between £50-100.

Current build:
AMD Phenom II X4 965 Black Edition 3.4GHz
8 gb kingston ddr3 1600mhz
Gigabyte GA-78LMT-USB3 760G
Corsair 600W psu

looking for a gpu that i'm likely to replace a few months down the line when i actually have some decent cash. i was thinking powercolor's 7770 for about £90 but i'm really unsure when it comes to graphics cards for budget gaming rigs. right now i'm running a severely fried gt 220 and even though it somehow competently manages to play games on the higher-end spectrum i need something more reliable.

thanks

 

[mein]

an extra £40-50 above £100 will see me like out of all my cash for the rest of the month. the quickest i can see about a £300-400 card will be about in 2-3 months.

the 6870 card i can find is about £110, which can be reasonable. it does seem a big improvement as right now i'm running a 1080p on 1768 x 992, and it does seem a hecka lot better in those benchmarks. is the £20 difference worth it though if i plan on replacing it in a few months?