Liquidware is an open-source hardware company, and they've got an offer for you: if you're willing to do some of the work putting it together, they'll sell you a tablet for $400.
To be fair, the DIY laptop kit isn't meant for computer novices just looking for an easy way to check their email on the couch. It's a modular system designed for serious geeks and developers looking to write specialized applications.
But still, it's certainly easier than getting the components and actually building a full tablet yourself. Instead, every component snaps on or mounts directly on the board, s you can choose just what you want on there. So if you're a tinkerer and are looking for a non-iPad tablet, this might be a nice option.