Well I said "at least" 8''. The bigger the better for me. I dint take that from Davinci. It seems to be the standard build volume I found in printers in the <800$ price range.
If you know of a printer with bigger print volume at that price range, please do tell me.

And you're right, I learned about the proprietary cartridges of Davinci after posting this. Since I've said here I'm also thinking of buying a Filastruder (or some other extruder, if you can suggest a better one), this printer is not for me.

Why do you recommend the Printrbot? Seems like Iphone of 3d printers to me. Overpriced i think.