they are not expensive... don't forget this thread is a few months old now. at the time, the $399 4G was the only one available. now you can get other models brand new for $250.
I can't see how your setup could be any smaller than the eeePC. your motherboard alone will be about the same size if not bigger. add the HDD, PSU, etc and its much fatter/thicker.
also, the eeePC is self-contained and fully assembled. your time is worth money too
