When you buy lumber from a sawmill owner to build your Hearthfire house, the dialogue says the lumber will cost 400 gold. However, the dialogue option shows up as soon as you have 200 gold and it will only remove 200 gold from your inventory, even if you have 400+ gold. This happens because the dialogue conditions and script use 200 as a hardcoded value instead of the global variable changed by Requiem.
Buy Lumber dialogue option appears only when having 400+ gold.
Buying lumber subtracts 400 gold from your inventory.
Dialogue conditions and script remain consistent with future changes of the lumber price global variable.
All other HF resource buying dialogues (e.g. steward) are checked for the same type of inconsistent behavior.