For what its worth, this is the ultimate calculus for a search engine; The revenue you can produce is proportional to your query rate, your query rate is proportional to your recurring user base, and your recurring user base is proportional to the usefulness of your searches, which is proportional to the number of pages in your index which is proportional to the number of servers you have running which is proportional to the cost of running the service.
One of the things I would have done differently at Blekko is that I would have created our own in house ad serving system (network) way earlier in the life cycle (Blekko never did have an in house ad network). It gives you better control over advertising latency and the quality factor of the ads. You also get to keep all of the ad revenue rather than just some of it. And you can deal directly with advertisers rather than the ad-tech crowd which can be quite scummy at times.
I wish you the best of luck in your endeavor, if you can crack the secret of surviving in a market where Google pays people over $4B/year just to send their search traffic to them, then you will be one of my heroes.