The Art market is interesting. That is an understatement.
A piece of art can hard to sell one year and two years later, it becomes impossible to find and the price has doubled or tripled. Why some pieces go from "cold" to "hot" is a mystery. Of course, some pieces go from "hot" to "cool" but rarely "cold"!
So, when does an art piece hit the "too high" price? Who knows! I wish I knew the answer.
Collectors, heed this advice: If you find something you love and have to have, buy it. It might unavailable and too expensive tomorrow.