I checked the website for this Little Wallet Card. This is what I came up with.
Little Wallet Card: $5.95
2 fat quarters, different designs
6" x 9" interfacing.
1 snap or buttom.
Considering the cost of the pattern, cost of fat quarters and interfacing, not to mention to snap or buttom, I would say $12.00 to $15.00 should be your minimum cost. Don't sell your self short, even with friends.