I'm not sure if this is a bug, but it seems odd.
I redesigned a branch to max capacity, increasing dealerships and employes, which reduced my expenses ?
See screenshots below.
They're taken 1 month apart.
Ok so I've reduced the monthly price increase slightly while at the same time increasing the starting monthly prices. The numbers should be a little more close. At least in early years, I'll do a test here in a second to double check for long term game play...
Anyhoo as such marking as "fixed"
After some longer term simulations it seems that changes in infrastructure have an effect as well.
I've made a minor change and flipped the values so that less infrastructure causes higher prices.
So you can think about "redesigning" reducing monthly cost by connecting to this "higher" infrastructure now.