TLDR; $20/mo, so likely no noticeable impact on traffic except -maybe- niches.
https://www.extremetech.com/computing/google-launches-ai-only-search-mode
The Next Web estimated in 2020 that Google made an average of $36/year (that's $3/month for those who are counting).
https://thenextweb.com/news/heres-how-much-money-you-made-google-by-staring-at-its-ads-for-20-years
I am going to guess that at least $0.50 of that is lost supporting the tech to serve all those ads. Maybe $1.
That means, for $30/yr, we could have ad-free Google. So now they are offering ad-free AI search for $240/yr. That's a big delta. Too big.
Of course, if Google were paid-only, no ads at all, then Bing would probably have most of the search traffic and it probably would be $240/year for Google search.
I might go $100 for a family plan, but I don't see $480 for two of us.
And by the way, I would not pay a penny for an ad-free version of Google. It's not the seeing the ads that is the problem, it is the fact that the search engine is optimized to maximize ad revenue not good search, which would be unchanged by a premium ad-free tier.