The cost of catering in Tournaments is dictated solely but your squad size , and there is no effect when changing chapters (unless you research a squad size upgrade in the new chapter)
The cost of negotiating on the regular map however, does jump up each and every chapter, and this has happened from Chapter 2, right through to the current maximum of Chapter 14. I believe that the reason you are only noticing the change now in Amuni, is that this is the first chapter where there is no Advanced Scouts, which until this point has been the first research in the chapter, which reduces the costs involved in fighting and negotiating on all provinces scouted after the completion of Advanced Scouts.
This was an intentional change by the dev team, as they felt it was wise to have a incremental factor that would limit the number of provinces that could be completed.