Peer to peer would be tough, you really need a 10G network connection to some tier 1 provider, and about 2500 machines to distribute the crawling/serving load. (that is if you want to do a full stack search engine). And while you can run that infrastructure for on the order of $100K/month (not counting depreciation) that means you need roughly $5K/day in revenue from that cluster. At $10 RPM ($10 revenue per thousand queries) you're looking at a minimum of 500,000 'real' search queries during 'English time' (roughly 7AM to 11PM GMT). That's 31,250 queries per hour or ~9 queries per second (average).

And that just pays to keep the lights on at the colocation center. If you're paying off the development costs (30 - 50 developers over 2 - 3 years) and the cost of an office somewhere. You'll want at least double that revenue or you'll go broke before you break even.

Ideally you are the 'go to' place for people looking to buy something as those queries make money. People researching Douglas Fairbanks for a high school essay consume queries but don't generate ad revenue.

It isn't for the faint of heart.