@Iluviaporos - I've actually seen a few schematics online for making printing hydraulic presses, which I'd be more interested in than just something to crush stuff.
I don't think they make nearly as much pressure, but it would be enough for the purposes.
I've also seen small, manual hydraulic presses in a museum I went to recently.
They were operated by a handle, and if you stuck a piece of paper under the press it would press a pattern into it, usually something related to the display you were looking at.
They were something for the kids to collect (although I enjoyed making them as well!).