For what it's worth, here's our take on this:
We bought some tiny labels at Office Max that are about 3/4" x 1/2", self-adhesive, about 1000 or 5000 in a pack. We write the price on those, then put that inside the lid of the box. Invariably, someone will pick up the box with their left hand, thumb covering up the price, then ask how much anyway. Maybe one day I will move those labels over to the middle of the lid!
You can also get hang tags at an office supply store. It's just a white tag, in various sizes, with a white string attached. You write the price on one side, and the type of wood or the type of refill used on the other. Then just slip the string under the clip of the pen.
You can also group like pens together if you charge the same price for each pen type. Like, all the Slims together and a sign saying $xx.
And remember, if someone asks, they are interested...take advantage of that dialog opening to sell, sell, sell!
Sheila