What i did was I took the levelcommon price, and kept it the way it was.
i then added the zombie_cost KVP and made it the same as the levelcommon. This seemed to work. I was able to see the correct price, and purchase it for that price, too.
I also removed any spaces i had in the levelcommon file, but im not sure if that has anything to do with it or not. I hope this works for you and anyone else having this issue!!!
Does your fix apply to the ammo price of normal and pack a punched versions? ive noticed custom guns such as skye ww2 guns will show the wrong price for the pap ammo wallbuy (supposed to be 4500 for all guns)