Any of these would do the job. The GTX 950 (and some variants of the others) require a 6-pin PCIE power connector and a 350W power supply.
GTX 750 Ti
RX 460
GTX 950
GTX 1050
Not all of these will be found for under $100, but figured I'd include them as they are near that price range. [strike]I'd say if you stick to your price range, the RX 460 would be the best option as it's better than the 750 Ti.[/strike]
*I forgot about the sales still going.