I did a similar item for a customer once, although it was not money. But the same concept should work.
Cut 2 sets of identical mats, with openings just slightly larger than the bills. Encapsulate the bills in Melinex, then assemble the mats with the bill showing inside.
For the upright frame, I used a 3/4" Studio black. Made 2 identical frames, then fit the contents with the necessary spacers to fill up the 2 rabbets. I joined the frames together with black head screws which I countersunk into the moulding. Remember to stain your countersink hole before you screw them together.
I used a larger LJ Antiqua for the base, but turned the moulding on end when I mitered it. If you measure correctly (which I didn't) the upright frame will fit into the rabbet of the base moulding.
The result is <a href="http://www.greyfoxgallery.com/img/framing/pennztester.jpg" target="_blank">here.</a>
I don't know why the hyperlink doesn't work.