Spawners that spawn naturally in the world can be picked up by using a silk-touch pickaxe by any player. Move them to make grinders, or to sell to other players.
/shop there is a spawner category. Save up for spawners that you need.
The spawner crate features rare spawners that can not be found naturally in the world. Keys are given as rare vote pinata rewards, or for donation.
Use the GUI to upgrade spawn delay, and spawn amount. The upgrades are meant to be long term investments, and are priced accordingly.