Mac gpu question

What is the most inexpensive Mac I can buy that comes with a GPU that supports geometry shaders?

There’s no telling what you can find on eBay. $599 is the cheapest that you can find on their store. i.e. You can’t buy any new Mac that doesn’t have support:

http://store.apple.com/us/product/FC270LL/A?mco=MTg4MjQ1MDU

Sweet. Thank you.