http://developer.yahoo.com/search/boss/boss_api_guide/faqBilling.html

How much free usage can I get?

Every BOSS API developer can get a credit of 50 BOSS Units of usage from the service. The free usage is applied as a credit to your account up to a month after your sign up date.

http://books.google.com/books?id=nUhiQxUXVpMC&lpg=PP1&pg=PR25#v=onepage&q=yahoo!s&f=false

Yahoo!'s 1k node HBase cluster used to host their snapshot of Microsoft's Bing crawl.

There, free for you. Problem solved.

Your little apps will never use up the entire 50 Search BOSS credits.

Update: sorry, I forgot some of you don't know how to use oAuth to connect to BOSS v2. Here are the libraries for various languages: http://code.google.com/p/oauth/

Seeing Microsoft make money off the little people while they bathe in Corvette limo swimming pools makes me sad and motivated me to post this info.