Up until 1982, guests at the Disneyland parks needed to purchase ticket books for most of the attractions. This was in addition to the price of admission.
Disneyland Ticket Booth 1970's
The admission, however, was much cheaper than it is today. In the early 80's, for example, the price was only around $12.
The attraction tickets were lettered from A-E. "A" being the less thrilling experiences while, progressively, "E" tickets were for the more popular, thrilling attractions. Thus, the often used reference to something that is thrilling or expensive as being an "E ticket."
The practice of selling attraction tickets was dismissed in 1982 and the price of admission has continued to increase. Today, Disneyland offers not only single admission tickets, but also multi-day passes and Annual Passes.