sales price calculation

Hello,
I couldn’t find it anywhere, so I’d rather ask you if it’s possible or not.

I need to set the selling price on my e-shop like this.

(Aliexpress price including shipping % margin) 3 USD (fixed amount)
example
(20 USD 30% margin) 3 USD
resulting selling price 29 USD

(Aliexpress price including shipping % margin) – I know how to do that, but I haven’t found a way anywhere to add a fixed amount to it, is there any way to do that?

Thank you for your answer.