Additional price and total cost

That is all custom code for that site. That site was initially built and developed by me, but that part is done by someone else. I do not know if that code is general enough to be shared. You could contact the owner to see if he is interested in sharing that code (probably for a price to recover some of the development costs he spent on that custom code).

But be aware that I do not have any plans to further develop this module and if you want a lasting solution, you would better go for BAT or Rooms.