The API is priced out with three tiers:
- Developer & Personal Use Plans
- Small & Medium Business Plans (up to 750,000 requests per month)
- Enterprise Plans (over a million requests per month)
The data within Wolfram|Alpha is rich and detailed, where many search engines, universities, businesses and individuals can benefit from on some level.
There have been rumors of a private API for a while now, some suspected a deal with Bing in the past.