If it is because of CUDA as you intent to run LAV and madVR I would recommend you go a bit above your $50 limit, as the GT 430 can be had for $55, and would be the lowest performance card to get for such a setup.
In the low end / mainstream video card arena, AMD generally holds the upper hand with a little better performance and also lower power consumption.
That's not to say nVidia is bad. I have a GeForce 9600GT in my HTPC. However, that was several months before AMD released the Radeon HD 4670 which I probably would have bought if it was available when I was looking for a graphics card.
Also, would any card give me the ability for some light gaming. No major game, maybe Sims for the girlfriend. Tv isn't a 1080p, only 720 if that helps.
Sims has been made so it is able to run on a large range of systems, from very low-end and up, so the GT 430 should be able to run it without too much trouble, and if you are going for a Radeon card 6570 or higher model, it would run even better as they are more powerful for the money at this price segment.