The cheapest route starts with the actual layers between the outside and the loot, not the largest wall visible from the road. Count each required target, then compare the whole sulfur bill.
Trace one complete route
Choose a path that reaches the objective and count every wall and door on it. Do not add optional splash targets to the baseline.
Compare mixed choices
The best item for one door may be wasteful on the next wall. A route planner can choose a different method for each target.
Leave operational room
Carry space, missed shots, failed satchels, counters, and repairs can all raise the live cost beyond a clean calculation.