Answers

What does it cost to post on X?

X charges per post created through its API, and a post that contains a link costs many times more than a plain one. The current rates are on X's developer pricing page. You do not pay that fee: each post counts against your plan in tweets and links, and X's per-post fee is Evenpost's cost.

X also limits how many posts one app can create in 24 hours, shared by everyone on that app, and how many one account can create in 15 minutes.

Evenpost is free during the invite-only beta.