This collection of sixty bottle caps from coca cola got quite expensive. They have the images of 30 Belgian sporters, and 30 Smurfs doing a sport, and they were obviously only available in Belgium. It was made in 1980, before the Moskou games. I bought this set with the collector map a few years ago for 6 Euro, and I thought that was about the price.
Apparently I underestimated the Smurf collectors or the coca cola collectors, as one of those sets just sold for 36 Euro... I'm glad I have mine already