You might want to look into Rocketrip (https://www.rocketrip.com). Their product is pretty much what you just described - you don't get straight cash, but you can get prepaid visa cards that get close.

Cool product. My flights are generally personally booked, and I basically compare as I described.

What I would like is an engine where I can punch in the various kinds of pain per hour I can tolerate and book that.