Cost: nothing. This guide is about the Free plan, and every step runs on a free ChatGPT account.
Ads show on the Free and Go plans, in regions where OpenAI's rollout has reached. Go costs $8 a month and still shows ads. Plus ($20 a month), Pro, Business, Enterprise, and Edu plans have none.
Nothing to install. Ads, when they reach you, appear below responses.
The rollout is gradual: on our US free test account (October 22), no ads appeared yet, and the Ad Controls panel isn't in the settings menu yet.