According to the Google Custom Search API Terms of Service:
Usage is free for all users, up to 100 queries per day.
Any usage beyond the free usage quota will fail if you are not signed up for billing. Once you have enabled billing, you will continue to receive 100 free queries per day. However, you will be billed for all additional requests at the rate of $5 per 1000 queries, for up to 10,000 queries per day.
So if I am reading this correctly, am I to understand that readers of my site can only search the site 100 times per day before I start getting charged for this service? If so, is there a way to construct this plugin without using the API? I ask because I know the Google Custom Search plugin only requires a Google Custom Search Engine. I just hate the way it looks, so I would rather use this plugin.