I think you will be amazed by how much better current graphics cards have become.
With Nvidia you can offload video from your cpu to the gpu using CUVID and MPC-HC.
$100 is enough to budget for a graphics card unless you are a gamer and then you may need a new motherboard and processor as well. Over $100 you are in gaming graphics card territory.
Madshi has indicated that new capabilities being rolled out in MPC-HC can utilize the newest Nvidia cards so this is a transition period. Waiting may bring more clarity.
I use an Asus GT 440, 1 GB DDR5 and have been very satisfied since installing last year in my 2009 intel core duo computer. I particularly liked not having to deal with ATi catalyst problems.
Many people are satisfied with the lower cost GT 430.