As I have been "into" 8-Track Tape Players and Tapes since they came out (and actually before with their predecessors, 4 Track Tapes and Players), and have an AM-8 Track for my 66, a Hang-On 8 Track for my 67 (so I could both the AM-FM Radio and 8-Track), a Hang-On 8 Track for my 66 T-Bird, and a Philco-Ford component 8 Track Player with original Demo Tape hooked up to my Marantz Amplifier, I have this "on my list" of Articles to do for the "Library". However, since I have other Articles that I'm currently working on, the 8 Track Article is "down the road" a little ways. In the meantime, I'll address a few things for gjz30075.
Jeff is correct in that Ford started issuing the 8 Track Tapes in 1966, the same year that they came out with the 8 Track Car Stereos. Ford issued these every year from 1966 through 1983, plus from 1976 through 1981, in addition, Ford had Quadrasonic 8 Track Tapes (like the ones Posted by gjz30075. I am lucky enough to have picked up over the years, at least one of each of the tapes offered to customers from 1966 through 1983, plus all but one of the Quadrasonic tapes.
There were three Tapes used in 1966 ; two were available to customers, and one was a 4 minute Demo Tape for "Dealer in house use only" - this one I am missing in my collection.
Jeff's other statement about these "not being in much demand, and therefore should be reasonably priced" is true for generally all the Tapes from 1970 up. The 1968 and 69 Tapes are generally 4 to 10 times higher, and the 1966 and 67 Tapes are generally "unreasonably priced" at $100-$200 each, or higher. The reason for this, besides the typical "initial offering scenario", is the Tape itself. To explain this, a little history is in order. In the early 60's, Muntz (of Muntz TV and Stereo fame), got the idea of making a unit for cars that would have music on a cartridge with a continuous tape, that could be inserted into the unit and play. This was a two-channel stereo system, and designated a "4 Track Tape Player" system. These were relatively small units (I had one that fit into the glove compartment of my 57 Ford Retractable), and took a cartridge that is almost identical in size to the 8 Track cartridges. Another "neat" feature is that there were many places available that would take 45 rpm records and put them on 4 Track tapes so you could have any music you wanted (and yes, I still have these). As "cool" as these were, sales were really not as expected. Then, Ford got together with RCA and Lear Corporation (yes, the same as the Lear Jet), and decided that they would produce a more dynamic 8 Track unit. Lear is considered the "founder of 8 Track Tapes". However, the initial Tapes (appropriately designated "Lear Tapes") proved unreliable, mainly due to deterioration of the tape pads, and resulting broken tape, and the design was changed. The Tapes available from Ford in 1966 and 1967 were of this initial design, and thus why the cost is high as finding a working or non-broken tape one, is not easy.
Enough for now. I could go on and on, but I'll save that for a future Article.
Hope this helps answer your initial inquiry.