You're not very explicit in your question about the trade offs you're willing to make, But you might want to think about this more:
I think the Google Custom Search might be an option but the daily limit of 100 queries is restricting. I would prefer to not scrape Google as it's a violation of their terms.
I've used google custom search, and it is very easy but the limit is in place. If you are concerned about not violating Google's TOS, this is the only way to go. You need to decide if you're willing to violate the TOS, and if not you should just use the google custom search.