One of the main reasons why OLED monitors are so expensive is that they are not mass produced in the same way as standard monitors. As they are less produced, these monitors tend to hold their value.
In addition to this, they have particularly high resolutions and refresh rates. When a monitor has higher specifications, they will be more expensive to purchase. This technology is also fairly new in comparison to other types of monitors.
As with any piece of technology, the newer it is, the more expensive it will be. As more of these monitors are produced, they will become less expensive over time.
OLED is a type of display that is very commonly used for phones. However, it is not typically used to create larger screens, mainly due to how expensive it is to be produced. Even so, there are types of monitors and TVs with this display.