Yale and Banff and Lido were the three old-time courses that were always talked about as having been enormously expensive to build.
In the past decade or two, expensive has been the rule and not the exception. Every course built out West that was sand-capped was very expensive.
Sebonack was a hugely expensive project ($100 million plus), though 40% of that was the land acquisition, and a bunch more went into the clubhouse and cottages. The golf course also cost way more than it should have, due to paying two designers and making expensive environmental promises and building things the most expensive way possible -- and, on top of all that, because it was in the Hamptons and you pay double for everything out there. But, even with all that, there are modern golf courses that cost twice as much to build as Sebonack.
P.S. You are just talking U.S. here. Pretty much every course built in Korea in the last twenty years, and in Japan in the 80's and 90's, cost $40 million or more to build. I just don't know that any of those count as "best".