[TYPO3-shop] How to let a customer to edit price in the basket view?

[Daniel Ciunkiewicz]

Dear List,
 
I'm searching for a solution which would give the customers a possibility to
edit the product price in basket view of tt_products. 
Could anyone of You tell me if it's possible? If Yes then how? 
This should be a solution for a shop with pre-paid elements and a user needs
to have a chance to set value in EUR for each element in the basket. 
Of course he can buy several elements and at the end he needs to recieve a
computed sum.
 
Thanks in advance for any feedback.
Best Regards
Daniel