Woocommerce and Gravity Forms problem with deliveries

Question

It's been a week since I'm trying to resolve this, and I'm just stuck. Please help :)

Here is the problem: I have a website with catering services, that are delivered every day to the clients. It's done using wordpress, gravity forms + addons (woocommerce and perk plugins with calendar and conditional pricing) with complicated conditional logic as the meals have different calories and so on. It's only one product, but it's coming from Gravity Forms itself. The form is calculating the number of days as a hidden field and I want to calculate the delivery cost by multiplying the number of days, that the Client placed the order for by the flat rate cost of a particular delivery zone in woocommerce (3 zones with different delivery costs in total). Let's say the cost of the delivery to one City is $5 and the order is placed for 10 meals, meaning 10 deliveries with fresh meal every day - so I want the delivery cost to be $5*10 = $50 for that order. I tried to achieve this with Gravity Perks- not possible, with Woocommerce Addon for Gravity Forms- it's possible to override the number of items ordered, but not the delivery cost itself... and I'm out of ideas :(

Does anybody have any clue how to achieve this? Huge Thanks and a big beer in advance :)