Cost calculator fr Word-Press Website

I need some kind of software for my website that makes it possible for clients to choose between between different product options and therefore calculate the approx. cost in EUR of the product. We make videos so it will probably look like this: How many days do you plan to shoot? (Dropdown 1,2,3). When you choose 1,2,3,.... it should calculate this position BUT if one chooses 3 days it should already add an additional day in post-production. So 1 or 2 days shooting = one day postproduction (extra position that "jumbs" in) 3 or 4 days shooting = two days post-productiion .... and so on .... The other positions like a professional speaker or licence-free-music are freely to choose. At the end the client should be able to calculate the approx costs of the video.