My Optoma ES522 keeps blinking all the colors of the rainbow and then going to grey. I have to turn it off four hours to even get it to start up again and then sometimes within minutes it happens again. What is going on, and how do i fix it? How much will it cost? And the project is now telling my lamp is at the end of it's useful life. How much will it cost to replace that?

My Optoma ES522 keeps blinking all the colors of the rainbow and then going to grey.
It seems that's the color wheel problem. You can fix this by your own. Probably the dust covered the color wheel sensor so it doesn't spin at specific speed.

And the project is now telling my lamp is at the end of it's useful life. How much will it cost to replace that?
You can switch off lamp reminder in OSD menu settings. This reminder is usually set to approx. 1200+ hours. When you exceed this limit, reminder starts to pop up. Actually it doesn't tell anything about PJ's lamp condition. So that doesn't mean that something is wrong with your lamp, maybe it lose some brightens, which is typical phenomena wheen exceeding half of lamps lifetime.

GENUINE new lamp costs around 160-180€, COMPATIBLE COPY should cost around 100€ +

Same thing here, same model.
When not turning on, just unplug the cord for a few seconds and then plug it in again, It will work. However, it will still be flickering after a few minutes or even seconds..