They have a few plans, but the cheapest is $5/mo. If you go past the allotted searches it’s pay per search after that (at a very tiny cost).
I switched to DDG when Google started adding cards at the bottom of the first page and made search results utterly useless for me. DDG wasn’t bad but it still felt like something was missing or some results were flooded by a specific site. Kagi went the extra step to group results from a site sorta like how Google has.
Ultimately it’s the benefits of old Google but some nice refinements and QoL improvements. Because it’s paid for, they don’t need to sell your data or shove paid for results down your throat.