Store your bills on the inside of your Minimalist Wallet!
If you have the card slots available and do not like the exterior money clip, give this a try. It's about 4 credit cards thick and should hold up to two bills…maybe three if the bills are fresh and flat.
Fold the bill in half, then in half again. Put the folded end into the bottom groove as shown in the picture. I suggest placing it on one end of the card deck. It does have a taper to it to make inserting cards against it easier.
No supports needed, I build up the overhangs across three layers and the bridges are so short, just about any printer should bridge this with ease.
.20 Layer height
25% Infill
3 bottom and 4 top layers