Unfortunately, you're not going to be able to run 3x24" monitors with the 570's you have unless you disable sli. So that kinda leaves you with the single 27".
Although, imho, if that was my budget, I'd swap out the 2 gtx570's for 1 or 2 hd7970's and go with the 3x24" asus monitors you listed, because if you're not going 3D, ati/amd does 3 screens better.
2xSapphire Toxic HD7970 6GB (@$699.99 each) $1399.98http://www.newegg.com/Product/Product.aspx?Item=N82E16814102997
3xAsus 24" (@$199.99 each) $599.97http://www.newegg.com/Product/Product.aspx?Item=N82E16824236153&Tpk=ASUS%20VS248H-P
Edit: Opps, forgot to mention, that with the above, you will also need 1xdp/dvi active adapter in order for eyefinity to enable the 3rd monitor