The GT 520 sucks. It is slower than a GT 430 which is slower than the GT 440.
The Radeon HD 6670 is best card for around $80. However, they are all PCI-e 2.1 cards. There have been a few complaints about a PCI-e 2.1 card being incompatible with motherboard that has a PCI-e 1.0 / 1.1 slot. Therefore, there is a small risk that you will need to return a Radeon HD 6670.
On average a HD 6670 w/ DDR5 RAM is about 10% faster than a HD 5670 w/ DDR5 RAM. You can compare the performance of these two cards and your GT 440 in the following review. The test rig in the review is using an Intel Core i7 920 @ 3.8 GHz. So your results will be different.
despite what everyone says a good under $100 is the evga geforce gt 520 2g, i have it and i can run swtor with all high settings and have no problems in warzone or high populated areas... i grabbed mine at best buy for $79.99