Adding a person should never be a decision anybody has to think about. Seat-counting is exactly what stops a team putting Finance, Legal and the PMs on the brain and those are the people whose reasoning nobody else can reconstruct. You pay for one brain shared safely, whether that is across your own machines or across the whole company. If you only need it on one machine, the local edition is free and always will be.
Unlimited projects, agents, tokens, recalls and storage on every tier. Fair-use caps notify rather than charge, because the whole thesis is recall before you search and write before the session ends and a meter teaches people to stop doing both. Agents and CI tokens are free and generous: a fleet of agents against one brain is the point, not the meter. Per head, that is $4.95 at twenty people, $3.98 at fifty and $2.50 at two hundred, against $20 or more a seat for most things your team already pays for. On your own it's $119.88 a year, paid up front, which is $9.99 a month. Two hundred people is the ceiling: above it, or inside your own perimeter, is Enterprise.
Signing up is self-serve and needs no card. Export is complete and free in both directions: ns-brain hive leave --apply puts every memory back into a local brain you own outright.