Ball chair  

bad
All replicas of that particular chair that i've seen are really bad , and most importantly , they are not cheap.
They are just aBOUT 20-25% cheaper than Adelta international.Ball and bubble are one of the few things that is really difficult to make them in a cheap way.even if you find one that looks good it is sure that it will brake very soon.That chair might look simple but in reality it is a very difficult project .The base...the angle of the opening....the swivel mechanism of such a big ball shaped thing that has to balance when somebody seats in.The oval versions/copies are more common as they are not difficuylt to make at all

I've seen some bad replica's...
I've seen some bad replica's too. The angle is wrong or the height is way off etc.
Is thatbecause they are to difficult to replicate or are there any rules or laws that prohibbit the imitators for making them in the right size.

The Sphere/ Ball chairs from...
The Sphere/ Ball chairs from Inmod and Krypton1 both seems like very cool and pretty decent reproductions. These reproductions are def. not cheap but still (at least in Europe!) 1/3 of Adeltas price and including the very cool feature - speakers!!
Check them out

Thanks, they look quit nice, ...
Thanks, they look quit nice, but the size and proportions are a bit different from the original. Is this really the best there is to find? I would like to know.

krypton
I have seen both the Krypton ball chair and Speaker egg chair and the fiberglass is really good. They are pretty much the next best thing to the real thing. I have seen some repos where the fiberglass looks so bad...
i would really think about the real thing though!
try mod livin for the Speaker egg chair if you don't want to spend the $ on the real ball chair.
http://www.modlivin.com

Inmod
The Ball Chair from inmod is pretty accurate for a reproduction. They also offer the same level of customization as Adelta.
http://www.inmod.com

I sell Ball Chair (Replica)
Hi, my company mainly produce and export designer chairs to European/US/Japan market. For example, the Ball chair just cost US$1150, Eames lounge cost US$950 (the above price include shipping to worldwide on Port to Port basis). If anyone interested, or want more pictures of the chair, please contact me at decorking@hotmail.com THANK YOU!!!