Hi, Marcos! Thanks for your question.
I would recommend you to use Elasticsearch whenever you need to make a search engine on your site. It gives a better experience to users: it’s fast, accurate and allows them to make mistakes in a query string.
As for the cost, it depends on the data size you want to store in Elasticsearch and the amount of search queries. I’d say that for medium-sized project it will cost you about 50$-90$ per month.