Algolia is a French startup that provides hosted cloud search as a service with lots of developer-friendly API.
What I like about Algolia is the speed, ease of integration with PHP/JS and the nice dashboard. Not forgetting the price is pretty reasonable as well starting from US$49/month (S$69/month).
Algolia also has free plans for community projects but the quota is a little low: 1,000 records and 50,000 operations per month.
They do offer higher quotas to selected open source and nonprofit projects and since I created a lot of WordPress plugins, I tried my luck to see if I qualify for it. After dropping them an email, I was pleasantly surprise that I am qualified.
I immediately switched over my custom search engine based on slightly complex MySQL queries to Algolia.
Algolia does query highlighting, so you do not need to perform Regular Expression (Regex) on your content to highlight the search query. You can specify the HTML class and element for Algolia to use to highlight the search query and you just have to style it on your own CSS file.
Algolia also does snippet results and you can specify how many words to return before and after the search keyword because you do not want to display a long wall of text in search results.
You can give it a try here lesterchan.net/site/search/ or the search box above.