I agree that prices should always be displayed. Put the price on the products and make sure you are targeting the right customers. If they go away just because of the price only chances are they are not a qualified target for your product. Customers looking for an $8000 coffee machine or shopping cart are very different from those searching for $50.00 coffee machines and free shopping carts.

Once you are very sure your targeting is reaching the correct customers you should see improvement in your conversion, however, if you dont see an improvement, then you could try an AB test that serves up equally a page without a price and the exact same page with a price. My bet is the response is greater from the page with the price providing the customer is qualified.