If it’s okay to go waaaaay back: salt. It’s always mind-blowing to me that people all over europe during the medieval age or even before that couldn’t season anything with salt cause it often was as expensive as gold itself. If I imagine those huge amounts of salt if you wanna pickle some meat or fish. Today salt costs nearly nothing, nearly everybody can afford it and it’s so basic that some even don’t consider it “seasoning” at all.

Wikipedia functionally ended the market for encyclopedias. When I was a kid I would go to the library and read an encyclopedia just to see what random knowledge was in there. Traveling salesman would sell encyclopedias door to door and they were hugely expensive. Then Encarta came along and it was mind blowing you could have all that information on some CDs. Then Wikipedia killed all of them and did it for free.

When computers began to take hold in middle class homes, one of the biggest gold rushes was to be the encyclopedia of choice on the computer, since consumers saw encyclopedia software as an obvious (and maybe best!) use case for a computer.

International phone calls. Actually long distance domestic phone calls too.

I always used to figure a decent desktop computer would cost me between $2k and $3k. That’s going back to the early 90s. But even though the value of a dollar has plummeted since then, you can get a decent desktop for significantly less, maybe half.

TVs are very cheap now. The 40" Samsung LCD in my basement cost $1,200 fifteen years ago. It will soon be replaced by a 43" Samsung 4K TV that costs under $300.

DVD players used to cost $500+ and are now practically free.

I pay $15/month for xbox game pass and have access to hundreds of games. I don’t own them but I can if I want to.

I love the fact you used LEDs as part of your post, because they themselves perfectly fit the topic of the post. Back in the 80’s and early 90’s, LEDs were almost prohibitively expensive. I can remember consumer LEDs in like '92 being over $2 a piece, which is a lot if you compare to today when you can get programmable RGB LEDs for less than a nickle a piece.

UNIX

AT&T, IBM, and a few others used to charge tens of thousands of dollars for it but Berkeley and Linus Torvalds both created kernels that didn’t use any of their code and pushed UNIX into a very niche market while open source UNIX derivatives took over the market. This is vastly over simplified but UNIX now has open source derivatives that anyone can use, modify, or distribute.

If you want to go way back, books were a huge investment. Before the printing press, each one was hand copied, which took countless hours for each one. Like, one book could be comparable in to the cost of a house.

I remember paying 5DM for a single blue LED. Which would be about 6 or 7 Euro adjusted for inflation.

I once paid a good months income for 16MB of RAM for my computer. Which put me into the category “the private home computer that has more RAM than all the companies’ servers together”.