Well, there are a few ways you could do it. Although, they would mostly involve sewing, unless you wanted it like a tube.....
first, you could make a long strip, fold it in half, and sew up the sides. Then turn it inside out.
Second, you could make two panels, sew three sides together, and turn it inside out.
Third, you can make it into a tube shape, using the flat circle crochet pattern. You need to start with a long tail, to use as a marker for the beginning stitch of each round. Here's the pattern:
http://crochet.about.com/library/weekly/aa091104.htmThis starts with a chain, but I usually use the magic circle technique (easily searchable on google). You can make the pattern as large as you want by just adding one more sc stitch in between the inc stitches. For example, you have the one round with 1 inc, 2 sc, 1 inc, 2 sc, etc. The next round would have 1 inc, 3 sc, 1 inc, 3 sc, etc. To get the sides of the coin purse, you do rounds of simply single crochet.
Fourth, you can do something with slip stitches. When you reach the end of a row, you join it with the other end of the row via a slip stitch. Then you chain, turn, and continue crocheting in the next sc stitch, skipping the joining slip stitch.