There are plenty of one-offs and custom performance ATVs in the world, but one of the truly rarest production quads ever made comes to us by way of Sweden and we have all the details here:

Rare ATV Sighting: Husaberg Enforcer - ATVConnection.com

 

That Husaberg is cool, but that is a pretty oldschool from the early 2000's tech.

There is also few other a rare unit's from europe, like this dutch company that looks really similar but way more advanced with a crf450r or YZ450R inverted engine

I forgot the name...CRQF or something

 

It looks like the crqf is close to $20,000. CRQF Quad | The new standard in quad racing

 

Until The Next Gen Honda TRX Arrives: Meet the CRQF - ATVConnection.com