Need a Form that calculates a price based on user input.

Hi,

I’m looking for weeks for a plugin.
I want a form that calculates a car insurance price.
the user must input the valuation and the age of the car.
and the form ouput the insurance price.
(i’ve done this in excel, but i don’t like to put this on my site.)

I’ve also search for a price quote plugin but didn’t find one.

i thought it could be done with gravity forms, but can’t find how to do this.

anyone can help me.

Thanks