You have $867,648
Total Cost: 60 (15x's on a single slayer arrow)
I click Order Improvements...
You have $867,574
867,648 - 867,574 = 74
After some more testing, I found that the blacksmith charges only $4 (the displayed price) for a single x. For 2x it charges $9. 3x it charges $14, etc. So the cost is off by $1 for each x past the first one.
I can only imagine that this problem compounds itself when multiple ammo pieces are upgraded at the same time.
