I think many people became well aware of the fact that hockey was an economic game in the 70s with the WHA. Perhaps if you were someone whose awareness of the NHL began post-WHA, it may have seemed that there was a loss of innocence with the Gretzky trade but I really think it happened earlier.
According to Peter Puck himself in his book "I'd Trade Him Again", he paid a sum of approximately one million dollars for Gretzky in the trade that sent him from the Indianapolis Racers to the Oilers.
It was a good book actually, Peter apparently also bought the Oilers with a contract on a restaurant Napkin (Moulson Brewhouse i believe), and used his wife's ring as a down-payment.
Hockey was much more econmical in those days.