Thanks Thomas, your review was extremaly helpful to reach the site from Kunming. Currently (November-December 2012) the situation changed a bit as there is an entry fee to visit the museum - exhibition (20 Yuan, which is not bad comparing to other places in China). Once you are there insist on opening the place of initial fossil's finding, photo attached (it is in the separate pavilion, usually closed, so you should ask the girls in the museum to open it for you, no additional fee required as this is part of exhibition).
Of course as a not-at-all Chinese speaking person I did not manage to get as good price for a motorbike as it was stated (For me that was 100 Yuan, I guess normal price for a 3-4 hours journey, that's the time you'll probably devote in the site).
The whole place is interesting, not well known by people in Chengjiang town (there are no signs of the site in the town)