They are not comparable at all. SearX only acts as a proxy to other search indexes. Kagi acts as a proxy to other search indexes as well + cache results + use AI to filter out dumb results + filter bad websites + provides summary on everything found + let you set websites to be high or low priority + provides several others services around. Kagi is a full end user experience comparable (or better) to what Google used to be in the past.
Have a look, there is 100 free searches when you register. Îve been a user of SearX, StartPage, Brave Search and others. None was of quality of Kagi to me. Note that Kagi is not yet advanced in privacy like SearX is (well for SearX is on private instance you are less to be privacy proof…).