There are a lot more original Transformers cels around than people think, they are just mainly in private collections now and are getting harder to find.

When I first started collecting 8 years ago, Transformers cels weren't that hard to find if you knew where to look, and atleast $150-200 or a lot more. 

There have been several Transformers the Movies cels on Ebay recently, but the auctions ended early, and probably sold for quite a bit of money off of Ebay. There are a lot of maniac Transformers collectors who will pay a lot for hard to find items.