As people are effectively only being charged for receiving a product which will be exactly the same when the website goes live, I think it is fair to charge a comparable fee to what will be used later.
ah, but theres the rub - it WONT be the same product when it goes live, as it will have benefitted from testing and the corrections of exposed (logic) errors.
I'd rather be incented to do their testing, than to be 'rewarded' in a few months time.
Its actually an industry defacto standard to acknowledge the time and effort in some such sort of way ....