Very nice finds, but I am curious on the value of cassettes? I wouldn't pay more than a dime for them. I may still have some sealed TDK. I'll have to check. I threw out all mine quite a few years ago. They were all recorded from records.
The price of that 10-speed back in the 70s seems outrageous. Was that around the time they were introduced? You can still get cheap bikes for less than that.