Here is the list classifying each between free, cheap, affordable.

Slack
Price:  Slack offers a free version with limited features, as well as paid plans starting at $6.67 per user per month. Affordable.

Microsoft Teams
Price: Microsoft Teams is available as part of Office 365 Business Essentials, which costs $5 per user per month. Affordable.

Google Workspace
Price: Google Workspace starts at $6 per user per month. Affordable.

Mattermost
Price:  Mattermost offers a free version with limited features, as well as paid plans starting at $3 per user per month. Cheap.

Rocket.Chat
Price: 
Rocket.Chat offers a free version with limited features, as well as paid plans starting at $3 per user per month. Cheap.

Zulip
Price:
Zulip offers a free version with limited features, as well as paid plans starting at $4 per user per month. Cheap.

Matrix 
Price: 
Matrix offers a free version with limited features, as well as paid plans starting at $3 per user per month. Cheap.

Riot.im
Price: 
Riot.im offers a free version with limited features, as well as paid plans starting at $2 per user per month. Cheap.

Zoom
Price: 
Zoom offers a free version with limited features, as well as paid plans starting at $14.99 per user per month. Affordable.
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