Nice question!!
My levels depend on the power of the device...
if is can function pretty much only as a reader or large PDA then $450 max...if it can also work as a true computer with most of the ability such as email, word processing (other office uses as well) along with running a complete OS like maybe Win7 and/or OS-whatever from Apple then $700ish if it uses an efficient panel like a PixelQi or even the larger Mirasol at around 10"-11".
I was not as impressed with the Edge and even less so with the MSI...the panels or maybe the OS just does not seem to leverage the dual panels well...my opinion of course...I could be wrong as we have only seen snippets of the abilities.
Right now, I don't see any larger format device which are any better than the DX or DR1000S (the current large-ish format device to compare against of course). These all are long on promise but nothing looks ready for mainstream use.