I understand wanting to save some money and get hardware that is a little older, but
the new GTX 750 Ti seems to be a great kh/$/w card now that cudaminer has been heavily updated. Look at this article
http://cryptomining-blog.com/tag/gtx-750-ti-cudaminer/ 6 cards do 1625 kh/s at only 432 W... and $139 a card. These are the R9 270's of NVidia.
I second this suggestion. If you can spend $160 instead of $100, you would do well to buy a 750 Ti card. The power to Kh/s ratio is very good for a GPU. If I could do it all over again, I would choose these cards.