Teamspeak is generally sold by usage slots.
There are many plans out there that start at the 10 slot level, some maybe lower numbers. What it means is that on a 10 slot server you can have 10 people online and talking at once. You can have as many people registered to use your server as you want, but only 10 can be using the server at once.
Check around, if your squad does in fact grow quickly, you may want to sign for a service that works off payments submitted by the members.
Underground Tournaments uses this type of system. What they do is to set up an account where funds can be deposited. The account is paid out of that fund.
http://myteamspeakhost.com/This outfit has generously donated Teamspeak servers to teams in the the scenarios on occasion. Not a bad way to go!
