Or a paid search engine incentivized to provide quality results rather than maximize ad network profits

Nice idea. But there's no sign that such a market exists. To put it into perspective, Google makes a nickle of ad revenue for every search. Would you pay that much?

I might pay subscription. I agree that the market is not likely to be big. Also data network effects and difficulty with price discrimination can be big obstacles.

EDIT: I think I misunderstood your question. I will probably pay that much for quality ad-free service. But of course it's a niche product.