Cost Effective Graphics Card for ProRender

After experimenting w ProRender for a week, I have found it to have surprisingly good performance for free software that is also nicely integrated with Rhino. It seems like a good potential stepping stone to build a portfolio and get some biz cash flow moving to be able to justify V-Ray and other high class tools.

I would like to ask Rhino ProRender users what graphics card(s) you have found to have good price to performance for general near-photoreal product visualization?

Best regards,
Bruce