The real cost
Unmanaged PPC does not pause while you wait.
Many Merch sellers already spend money on Amazon Ads every month, but the account is not reviewed with enough structure. Weak products may keep receiving clicks. Search terms can stay messy. Old campaigns continue running. Promising products may not get graduated. Bids and budgets can drift without enough context.
Monthly PPC management is not about forcing more spend. The work is to manage the money already moving through the account with better review discipline, cleaner structure, and more consistent decisions. The cost comparison is account-specific; this section describes management risk, not promised savings.