$40 is cheap, but I don't know anything about Buffalo or the vendor you link to. Most small print servers I have seen from the major vendors (Linksys, Dlink) are $70-80. I am surprised how expensive they are. With 2 computers, it almost seems to make more sense just to get another printer.
What would be really useful is a "Y" cable so that two coumputes could be hooked to the same computer. It shouldn't be too hard to avoid printing at the same time. Has anyone seen anything like this?