Product with attribute without price

[bonsaiko]

Hello,

I'd like to know if what I have in mind is possible to do:

I have a product (which is a book) that has an attribute called "book type". 

This book type can be:

- paper book

- digital version

- book for blind people

For the 2 first types, it's ok, I have a price for paper book and another price for digital book. 

But for the last type, which is for blind people, the book cannot be paid on the site because the price is not fixed. So I want no price to appear, and the customer will only be able to order it, and not to pay it. 

I'd like to know if it's possible, and how I can do this. 

I already tried to put 0 as the price but it's not working.

Thanks