I think an entry level professional graphics card could be what you're looking for, they're just slightly more than you said your budget was. They start from about $100 USD but they have plenty of driver and customer support.
I think you should pay a small cost and buy an entry level solution from AMD or NVIDIA.
I would recommend this http://www.nvidia.com/object/buy_now_results_ci.html?id...
Notice that there's PCI, PCI-e x1, and PCI-e x16 cards.
Not sure but, I would be more concerned with a RAID chip or LAN stealing CPU cycles than the video card.
Probaby best to just buy a cheap graphics card for 50 usd though, they have drivers for windows 8 too.