Another discussion of how to determine prices:
Price influences behavior. In order to craft an excellent user experience, the price — and how your users interact with that price — must be central to the development of the product, especially applications. No user will welcome an application if the cost is prohibitive. This makes price every bit as important as design, information architecture and wireframing, and it goes deeper than just getting people to click “Buy.” By focusing on users in setting and maintaining a price, you will increase revenue, lower overhead and, most importantly, significantly improve the user’s (read customer’s) experience.