As a Sitecore MVP, I have used Coveo in my Sitecore projects as a simple way to get search up and running. It is a powerful tool and you could start off with free edition and then upgrade to Pro and Enterprise to make use of additional features.
Now that it is available for Salesforce, I am definitely cheering and you should too. There is no excuse now that the free edition is available. Start out with the free edition, see the power and then as needed upgrade.
Check out this article for more information on Coveo free AI Powered search for Salesforce