I believe there are 50 different colors in the complete construction kit. I am missing 8 colors from my set:

1, 2, 3, 7, 8, 18, 27, and 29.

Singles have sold for very high prices in Saito auctions in the past. I'd pay $5 a color (3 pieces) for those I'm missing.

My set cost me less than $100 several years ago from a collector, not from a salesman. However, the set you show appears to have multiples of each color, so would be worth a premium.