Customize Virtuemart 1.1.9 shop with specific calculations for touristic products

Hi, I need to finalize a project that another Freelancer did not finish. The VM shop offers booking service for hotels, activities, holidays packages and car renting. I need several calculations in ajax for each type of product in the flypage, but this project will start with the activities products. When this step will be ok I'll ask the freelancer to achieve the others tasks. I join a picture to explain the process clearly, but the big idea is to have advanced attributes to be multiplied by custom attributes in order to calculate a total amount displayed in a custom attribute and then this total amount to be added to the cart. In realtime, using Ajax. Thanks for yours bids !