From the builds we have scoped, three levers move the number, and none of them is the chat itself. The first is integration: a bot that only replies sits near the bottom of the range, while one that books a table, looks up an order, takes a payment or pushes a lead into your CRM costs more because it does real work across your systems. The second is custom logic: the more decisions the assistant has to make on its own, the more there is to build and test. The third is message volume, which raises Meta's per-conversation fees as traffic grows.
This is also why the cheapest option is rarely the right one. A subscription bot is fast to switch on, but it rents you generic answers and stops the day you stop paying. A focused custom build aimed at a single expensive problem, the kind of AI automation that replies in seconds and captures the lead, usually pays for itself before the full multi-system version is even worth discussing. If you are still weighing a tool against a build, the WhatsApp chatbot buyer's guide walks through when each one wins.
