According to Maccas the 1990 mint set has a current retail of $120. This makes it the equal most expensive mint set.
My question is why?

Lets look at some figures.
Mintage is 103,766. Thats higher than most modern year mintages.
$1, 50c & 20c were all mint set only. But they were in 1989 and 1992 as well.
So why is it so expensive?