No. Google Maps Ads are not free. They are part of Google Ads, so you pay based on the campaign type and bidding model. For example, Maps ads can use click-based or view-based charging depending on the campaign and ad format.
What is free is your Google Business Profile, which allows your business to appear organically on Google Maps without paying for advertising.
So, the simple distinction is: organic Google Maps listing = free; paid Maps advertising = requires an advertising budget.