Frugal

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

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.

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.

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.

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.

FYI the cheaper LEDs and usb power outlets are all disposable quality. Prices on the high quality stuff are coming down because of the downward force of cheap shit, but the really cheap shit is cheap because it's shit.

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.

Along those same lines, I would say LCD monitors and TVs. Obviously they are not "cheap" as in pocket change, but they are an order of magnitude less than when the tech was introduced.

Also computer storage, e.g. SSD drives and SD cards. (Although maybe it's cheating to cite anything related to Moore's Law.)

Embedded computers.
It used to be that everything got a custom or at least customized circuit board, and fancy wifi or Bluetooth functionality, or smarter programmable features would make that really expensive.

Recently, the cost of embeddable system on a chip setups has dropped low enough that it's typically cheaper to put more computer power then you need in a device than to make something custom.

It's why everything has wi-fi and Bluetooth now. It's cheaper to use the prefab piece, and those all come with that build in, so you may as well advertise it.

Not too terribly long ago, clothing was super expensive. Like, make a dress from burlap or old feed sacks instead of buying something expensive. Some companies that sold feed and seed would print floral patterns on the sacks because they knew customers would turn the old sacks into clothing for their children.

Digital calipers. I have a pair of high quality Mitutoyo calipers from a long time ago that cost $250 and some from eBay more recently that cost $15. Honestly the $15 ones are nowhere near as good, but definitely usable. I'm assuming some in say the $50 range could be just as good as my expensive ones.

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.

Lots of old cars. You can get 80s and 90s Rolls Royce for very cheap from private sellers. Some late 70s / early 80s Ferraris (like the 308) can be had for under $10k.

Mind you, they're still incredibly expensive to maintain and thus not terribly practical, but the cost to entry can be far lower than most would think.

Typically things they can they can tack subscription fees onto

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".