It's interesting that Microsoft is planning to charge more than Yahoo! Boss for access to the same data. BOSS charges $0.80 per 1000 queries, while Microsoft is priced at $2 per 1000 queries. BOSS is also pay-as-you-go with no monthly minimum. BOSS has less restrictive terms and conditions (re-ordering allowed, for instance). I've been using the Bing API instead of Yahoo! BOSS for my metasearch engine for two reasons: the feed is free, and the response time is faster. The Microsoft/BOSS prices are not unreasonable if you are actively monetizing your page with search ads, but if you are doing an experimental search engine it is very stressful. If I suddenly get a surge in traffic, I could be broke very quickly.