Just ordered myself the third 23.6'' ASUS monitor from Newegg and a Accell DP to VGA adapter from Amazon.
I got the idea to get an Accel adapter from the AMD approved eyefinity adapters. Although I couldn't find any of the approved ones, but this one is awfully close. I was looking for the B101B-003B model but could only find B101C-001B. I don't know what the difference is, but i'll let you guys know how it works (if it does). It was only$40 shipped. Much better considering the DP to DVI prices!
More abouteyefinity dongle work
As long as the resolution isn't more than 1920x1080 (which I don't think those Asus monitors are) it should be ok- I've not tried it, but there are a number of people report good results from the DP to VGA dongles.