Jim:"Craigslist uses a 3 tier architecture:Cache->Web->Database and deploys approximately 200 Intel-based servers built to our specs with a LAMP (linux, apache, mysql, perl) framework. Mod_perl , mod_gzip; 175,000 page views per kilowatt-hour" (answer to forth question)
and they have 24 employees... and "approximately 7.5 billion" pageviews per month
(answer to sixth question)
you'd think anybody familiar with the type of business should have no problem figuring out how much does that cost...
P.S. Again,(P.S. for that entry), Donna deserves credit for having gotten a more detailed breakdown of what it takes to run craigslist than I've previously seen... D.