yeah, there aren't many alternatives unfortunately. I've used Sphinx a lot, but am now stuck with ES and it is horrible to operate, probably because we don't need a cluster solution so it is total overkill. Yeeeah for technical debt.

For small projects (for some 1000s of documents), I'd probably go with Postgresql FTS if possible. Sphinx/Solr for anything with indices smaller than a couple 100GBs After that, ES seems reasonable & worth the overhead

EDIT: my biggest issue with ES is that it seems to be specifically engineered to sell you support. So get a managed version if you can.