Quite frankly the pilot is not the most expensive thing on that aircraft. A 737 burns $2100/hour of fuel at cruise, more during takeoff. Total operating cost of a 737 might average $4000-8000/hour factoring in all costs. And you want to save $400 by not having a crew?

Also the average payout for an aviation death is like $5-10million. So you’re talking about something like $1 billion in wrongful death liability alone per aircraft. Your insurance carrier isn’t going to be happy about that decision to save $400/h in crew costs. So whatever those premiums go up by has to be less than the $400 you’re saving.