Custom customer text input, price by letter, but no price for whitespaces

[macsek]

Hi!

Sorry for the poor english.
I would like to make a product, that has an input field, and customer must pay for each letter, BUT it would be nice, if the whitespaces should not be paid!
I checked almost the whole source-code, but can not find where the price is calculated from the length of the field, so I cannot change it.

Can anybody help me?