Two forks decide a suite budget: the ceiling and the deployment
Broad business suites are usually priced per organisation with a cap on users, and often offered as either a hosted service or software you run yourself. Those two choices, not the headline fee, determine what you spend. A user ceiling turns hiring into a re-pricing event, and self-hosting moves cost off the invoice and onto your payroll.
Map the ceilings before you plan headcount
Ask where each user ceiling sits and what the step above it costs. Then place your current team and your expected team on that ladder. Sitting one person above a boundary is the most expensive position in per-organisation pricing, and it is entirely avoidable if you know where the boundaries are.