what is the cheapest video card that supports directx9.0c and is t&l capable?
That will depend on where in to world you are and the type of graphics slot you have!!
It's not worth it to get the cheapest card, as they are really really terrible. I recommend getting either the PCI-E or the AGP version of the 7600GT, as that is a pretty good videocard and will play most games on high settings.
Just get a 6th gen card from ati or nvidia,,
You can get a geforce 6200 for fifty bucks ,,