Actually Yoichi Kotabe did the character design 
although Miyazaki did work on other aspects of 
the animation process (and the director of the 
series was Isao Takahata) but this wasn't his 
sole project. Heidi was part of the World 
Masterpiece Theatre series -- you may have seen 
cels from Anne of Green Gables which is also one 
of the series produced.

Other animators (such as prominent Ghibli 
animator Katsuya Kondo) are often confused with 
the Miyazaki style. For example, I see a lot of 
cels pop up on ebay for another World Masterpiece 
Theatre series, Nan and Joe (character designer 
Sato Yoshiharu who was the supervising animator 
on Totoro and Omoide Porporo). They are often 
=wrongly= associated with Miyazaki. 

Check out www.nausicaa.net for more information 
(they have such a great site!).

I would imagine the prices reflect hanken quality 
cels (although I know a lot of Europeans who grew 
up watching this version of Heidi on TV -- I 
think in Spain but I could be wrong -- so that 
might account for some popularity). I'm not sure 
what "for exhibition means." 

Wendy