Graphics cards do not have USB3.0. You are thinking of sata 3 which makes little difference in performance or compatibility.
$80 might buy you a 7750 which is the bare minimum to be considered as a gaming card.
What resolution are you playing at? For 1080p you are going to need to spend a little more than 80 dollars for something current. You might be able to get a gtx 280 on ebay for around 80 bucks.
A 280 will play most games at 1080p on medium settings, depending on the rest of your parts. The cheapest current gen card you can get to play games is a gtx 650 or hd 7770, these cards range from 100 to 120 dollars depending on the vendor.