Why do arrangement costs look different from the library?

The short answer

Because the event arrangement is not just a live view of the library template. It is an event-specific record with snapshotted pricing and event quantities.

What commonly changes the total

the event quantity is higher than the base template quantity
current item prices were snapshotted when the arrangement was added
rental calculations depend on the event date window
event-specific edits or substitutions changed the arrangement after creation

What to check first

Compare the event quantity against the original template assumption.
Review whether rental duration is affected by the event dates.
Check whether someone updated items, substitutions, or pricing snapshots in the event arrangement.

Why BloomBoard behaves this way

The event arrangement is meant to protect live commercial work from silent changes in the master catalog. That means it may intentionally differ from the current library state.

If the event version is wrong, correct the event arrangement or refresh the pricing workflow before sending a quote. Do not assume the library total is the customer-facing total.