Karl's questions are the ones I would ask...
They also highlight the advantages of validating with prospective customers all along. This is one great reason you do it so that you have a list of potential beta customers who have already told you how they would evaluate the pricing, etc.
I suspect you may have done this...Bravo!
You should also then add a few more "cold" ones...those that have a similar problem to those that are willing to be Beta customers...this will test out what your sales folks might see with a new prospective customer (in contrast to the pipeline you've been developing as you developed the product).
And of course I agree with all of the others...the price should NEVER be $0. You can have a free trial, a money-back guarantee, a discounted price or extended initial term, etc....but if they are not willing to pay for it, why both with them...and if the "free" people are the only ones you can find to try it, perhaps you do not have a business opportunity worth pursuing.
...or perhaps you are in an very unusual situation, and you can justify "free" for some very unique reason...better be a real good reason!!!