Dynamic price addition to product

Hello,

We are working on an addition to the product to allow product embroidery on specific products. For this we added an item custom field with modification and we would like to add a price to it. The cost of the service is defined by the amount of chars (letters) and we would like to calculate the number of chars and add the price in accordance.

Ciould you please advice?

Thank you,

Guy.

Thank you Nicolas. That looks spot on
Will give it a try.