Total cost of this build was less than $1 in materials. It's a very simple project that yields a pretty cool result.
I made it at TechShop.
A quick note on safety: We will be using some of the tools commonly found in a metal shop, including shears and bench grinders. When using these tools, make sure you have no loose clothing. Do not wear gloves as they can easily get caught. And, as always, wear safety glasses.
Step 1: Gather Materials
16 gauge is probably the thickest you'd want to go. I think 22 gauge would work just fine.
Step 2: Cut Your Piece to Size
Step 3: Clean Up the Edges
Step 4: Bend It to Shape
The first is to add a lip to one end. The curved surface makes it easy to slide bills/cards into and out of the clip.
After that, you'll just need to bend the remaining length in half. Look at the captions for the photographs for additional comments/instructions.