Yep, we do use the Bing API.
https://www.microsoft.com/en-us/bing/apis/pricing
Thats like 30-searches per day (including any tweaking). How can a solo developer make an MVP based on this?
Interestingly, the very existence of the new Bing does us a favor in this regard -- it warms people up to the idea of using something other than Google, even if it's just for a subset of searches.