Good day
I have studied your request in depth, and understand your requirements.
With my limited knowledge of the Danish language (that is, nothing :) ), I manage to figure out your requirement. OK, I cheated, I used Google Translate.
Basically, you have a set-up/installation fee (“Oprettelse”) and a monthly rate (“Månedlig ydelse”).
For 1-4 users, your setup fee is green, DKK 1290. For 5 and above users you add an additional fee, the purple, DKK 645.
Then, then monthly rate is added per additional user. These are also colour coded.
These colour combinations will be in a select list where the user selects their requirement, and based on this selection, calculation will be done and the total costs shown in a side bar block in real time.
From the side bar block, a button (ex: “Place order”) will take you to the Quickpay payment system. I have already checked, there is a Drupal module for Quickpay.
I understand that the same system should be reusable over different pages where required.
Despite my jokingly introduction, I hope you can see that I have a clear grasp of your requirements.
I'm fairly new to freelancer.com, but I am not new to Drupal, I have been working full time with Drupal for over 5 years. I have written many customs modules over the years and have published modules on Drupal.org. I strictly follow Drupal's coding practices.
If you have any questions about me or want to discuss this further, please feel free to contact me.
Regards
Quentin Campbell