Nothing is ever in stone. However, if by "my PH" you mean a friend as well as operator/guide, then I would hope he is getting you the best deal he reasonably can.
The Caprivi is special place to hunt. The buffalo in my avatar came from there, and it remains the most beautiful part of Africa I have hunted. It is essentially an extension of the Okavango delta habitat. Unfortunately, that paradise like environment, combined with limited quotas, and some very fine bulls make it a fairly expensive place to hunt a buffalo. Jamy Traut is one of the best known outfitters hunting the Caprivi (and other places in Namibia to include the Waterberg Plateau where some of the largest bulls in Africa are taken - and priced accordingly!). He fully lists his prices and they will give you a good measuring stick against what your PH proposes.
https://jamyhunts.com/
I should add that I hunted my first bull with Jamy and you could not expect a better dangerous game hunting experience with anyone else.
You will likely find "all in" costs may be a little less in Mozambique and Zim.