>I think it is genuinely difficult
Yes. It's difficult to say, but you can make estimates and they have been done. Estimates made by economists are better than wishful thinking.
>You could see 40 years of extraordinary technological and economic progres
We don't have time. We have used our carbon budget. Doing things in hurry is what increases the cost.
To stop global warming below 2 C requires that our emissions are cut into fraction of current levels within 15 years. That's incredibly short time. We should be shutting down coal plants already and companies should write off their investments. There is no time for smooth transition.
Major estimates agree that that avoiding climate change is affordable can can be done, but time has run out (not running out, has run out). U.N.’s Intergovernmental Panel on Climate Change estimates that the cost would be 13 trillion trough 2030 using idealized scenarios. It would reduce GDP just 0.1%. Big task but clearly affordable. The bad new is that there is no sign that there is will to invest even close that much. There is no political will to do that. IEA estimates say that the cost is around $30 trillion.
Things like GOP's "clean carbon" policy take out the possible and all idealized scenarios. There is no change in hell that GOP ruled House does anything significant to make "perfectly possible" happen. 4 years from now cost has increased again.
>I think ultimately we just have to do our best to price in the externalized costs and to a certain extent to set the hard limits of the amount of damage we are willing to inflict, and let the economy adjust to the reality of the situation.
Yes. I think 4 degrees is what is going to happen. Horrible cost for humanity and nature. Show your kids coral reefs when they are still there.