A website budget should include the period after launch. Maintenance is the cost of keeping software supported, content accurate, forms working, backups recoverable, and small improvements moving.
Separate predictable and occasional work
Predictable work includes updates, monitoring, backups, and routine tests. Occasional work includes new pages, integrations, redesigns, accessibility improvements, or incident recovery. Keeping them separate makes a proposal easier to compare.
Budget for attention
The cheapest plan is not helpful if nobody checks whether a backup can restore or whether an important form still arrives. Choose coverage based on the business consequence of downtime.
WordPress maintenance can be scoped around your actual risk and workload.