BOSS queries are $0.80 per thousand queries, so $0.0008 per search. A web search site that uses a premium sponsored link feed should be able to generate about $0.04 per query (50% share of the $0.09 per query that Google makes). Thus the revenue generated could be about 50 times the cost of the raw materials (the BOSS search results). BOSS is cheap in that regard. If you extrapolate to an entire year, DDG could be making about $15 million per year in revenue if they chose to show ads aggressively.