As of today, the Bing Search API is now being offered on the Windows Azure Marketplace.
For up to 5,000 queries per day, developers can use the API for free to query Bing for web, image, news and video search results as well as related searches and spelling suggestions. For queries over 5,000 developers can subscribe to various tiers of queries per month. For instance, 10,000 queries is $20/mo and 20,000 queries is $40/mo (all the way up to 2.5 million queries per month).
The new Bing Search API supports both XML and JSON formats.
It is also worth noting the features that are included in the Microsoft Translator API which is treated separately than Bing Search API.
Microsoft Translator allows for the automatic machine translation of text into specific languages via web service API. For up to 2 million characters per month, developers can translate text for free. Moving up to 4 million characters costs only $40/mo.
Microsoft Translator API
Transition your application to the Windows Azure Marketplace:
1. Sign up for the Marketplace.
2. Read the migration guide on transitioning your application. You can expect the transition to involve targeting a new API end point, moderate changes to the request and response schemas, and a new security requirement to authenticate your application key.
3. Subscribe to the Bing Search API and create an application key. You will not be charged for API usage until the trial period expires.
Important note…the Bing Search API 2.0 will be decommissioned on August 1, 2012 so existing developers are encourage to migrate their applications as soon as possible.