You can buy the Slim Clip on ebay for about $1.50, including shipping from Hong Kong. In my opinion its well worth that price, and you could buy several for spares or gifts.  It is a "made in China" product, stamped out of stainless sheet steel, then folded into shape and tempered to retain some springiness.

One caveat - the stamping process leaves burrs on one side of the metal blank that isn't ground off by the manufacturer before the blank is folded into shape.  Not to worry.  You can (and should) take a small grinder (like a Dremel tool, or I use a $5 grinder from Harbor Freight) to grind the burred edge smooth.  The burr is all on one side (if it were flat) and is caused by the edge of the blank shearing out of plane as the stamping tool presses the blank out.  Use half of a wooden clothes pin (or equivalent) to wedge the clip open on each side, and just follow the burred edge around with the grinder until you wind up back where you started.  You can feel with your fingertip if you got the all burr off.

Once you have deburred it, it is, again, in my opinion, a very good clip, and holds cards and bills firmly in place.  If you don't deburr it, i think you might suffer scratches on your cards, or even tears on bills.

The card holder has the sides turned up to prevent the cards from sliding out sidewards.  I use my drivers licence as the top card, with my picture showing.  When I pull out a credit card, I pull them all out together, because the raised lettering on the cards makes them stick together in the clip.  I also use a card with bills folded over it to insert bills, otherwise the bills want to bunch up under the pressure of the clip.

A good buy at buck and a half, but not worth much more than that.