Attribute price factor for total price

Hi all,

I have a product that is priced by attributes. The important attribute is text where the user is charged £1 per letter with 2 free. The text also has an offset of £1 making a 2 letter product £3, 3 letter product £4, etc.

I now want to have an option for vertical text which adds £0.25 per letter.

I have tried all the options I can think of but can't seem to get this to work. I would *really* appreciate any help that could be provided :flex:

Cheers, Lloyd.