Even if you made your own board, you would still have to populate it and adding a regulator to the EMSL board would only be a few dabs of solder.
There is also this, again by EMSL: http://evilmadscience.com/productsmenu/tinykitlist/180-diavolino
That's a more expensive kit but comes with a '328, crystal, caps, reset etc (and space for a regulator but it's a TO-92 packaged one). Still less than a full Arduino but no prototyping area.
I have bought empty Ardu' boards for £1.50 each off e-bay and populated just what I need but again there's no prototying space.