That’s an interesting question!
Unless I’m mistaken, though, it is not something that EDD itself supports “out of the box” and so you’d have to approach it as a customization task where you cover a number of areas not just in our plugin but EDD itself.
Our Themer’s Guide covers the basics of safely overriding and customizing our templates and, in this case, it is the eddtickets/tickets.php template you would be interested in (if you want customers to specify the price right in the single event ticket form).
I’m afraid though a change of this nature is beyond what we can guide you through here on the forums (though of course if you have any more specific questions relating to our plugin feel free to ask!).
Thanks again 🙂