It isn’t for small sites (you can always check pricing and features of each plan at Discourse pricing | Discourse - Civilized Discussion). If the Algolia plugin is needed for your small site, our hosted plans won’t work for your community.
However, small communities can use self-hosted Discourse, where you’d also be able to use the Algolia plugin. 
The self-hosted instructions are available at discourse/docs/INSTALL-cloud.md at main · discourse/discourse · GitHub. 