Selling price control

Our products can be standard or special products . so what we need is to make a select custom field which contains standard - special .
by default it will be standard but if the user select special it should update Selling rate by price list rate * 1.3

how can we do that ?

I think it would be a better option to go create two separate items. A-Standard, A-Special.

Hi have you tried the price lists and pricing rules? Maybe this link is a good place to start exploring.