Create an account on Air France KLM Flying blue, and check for awards there for your SFO-AMS.

Just a few days ago, I was able to book a one way SFO-CDG for 18,750 + $79.56 as a promo award, in November. I think a regular award is 25,000 miles.

Indeed, you cannot book 1-way cash fares between US and Europe - or rather, they cost 4x the price of a 1-way, so it never makes sense. The 1-way flight I booked would have been $2687 cash fare. Or $726 round-trip.

This is where having the Chase UR points, and the ability to transfer, helps the most, IMO. The 1-ways can be booked at prices that make sense as award flights. Not as cash fares.

You don't have to choose the same airline for your return - you could transfer some UR points to one airline, and some UR points to another, as long as they are Chase UR partners.