Swiftype would also have been my preference, but now their cheapest plan starts at $299 per month, with no more free or cheaper plan available (ref. "Swiftype silently drops free plans").
An alternative that currently does have a free plan is Algolia but from what I understand you'll need to provide the "schemaless objects" yourself, which is way more complex than I wanted to make search for myself.
What I like about Swiftype is that they crawl your site and create the search index for you, with no hassle. That's especially helpful for people with static hosting (e.g., S3), since tools like Bleve need a server.
Quality of search engine
Furthermore, Swiftype are "search engine creators" themselves and will probably improve the search tool themselves. The quality of the different search engines seems to be overlooked in this discussion, but I think this is quite an important point.
If I look at Bleve, then I see that searching for "search" returns results that do not include "searching", and when using "searching" as the query then none of the pages that match "search" show up. In other words, Bleve doesn't consider "search" and "searching" synonyms and that's a problem I think.
(Case in point, Google lists the current topic as the first result when searching both for "hugo site search" and "hugo site searching", and I believe that a good Hugo search engine should do the same.)
DuckDuckGo slow to index
The problems that Stiobhart mentions with slow indexing with DDG is also something I experienced with that search engine. So the only way to reasonably simple implement searching for non-Go developers seems to be Google custom search.
Does perhaps anyone know about a Swiftype alternative (free or affordable) that manages the searching for us?