What's the cost of shipping on a single resistor from mouser or digi-key? Can you buy <15 from Amazon? Another way to think of it is that the ability to have no minimum quantity, not having to wait for shipping and maybe, if you're lucky, someone who can help you with info if you need it is baked into the price. With that in mind, maybe it isn't as overpriced as it seems.

Amazon didn't exist at that time (or was probably still only selling books). Digi-Key still had a $25 minimum order. RS was pretty much the only game in town if you were a high schooler with a small allowance.

OTOH, some items were surprisingly cheap. A couple years after college, I had a small business running out of a spare bedroom making temperature monitors and there was a shielded audio cable with connector that I used for the sensor. Radio Shack's price was about $1.50 each but all the "real" parts houses were at least 5x that.

I don't buy a single anything from those others. I'm going to buy enough to meet their $40 minimum order. Shipping isn't free, and takes 4-6 weeks (remember this is 1960-1990). All this means that I'm planning all my projects months ahead to make a large order that will keep me busy several months (starting 2 months from now)

As an engineer my boss will approve $80 for a single resister after overnight shipping if that is what I need. The factory is buying the resisters a reel at a time (or similar large quantities)