Frugal

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.

I mean sure if you are talking leds but if your talking light bulbs in general then they are way more expensive than back in the day. Anything before mass production is more expensive than after but if you mean something that was basically mass produced but got cheaper then I think that has happended sometimes when a better process comes along. Gas is pretty cheap now relative to inflation.

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 cases for a computer.

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.

TVs. I once paid ~$300 for a 32" CRTV. Now I can get a 55" flat screen for under $100. It's weird.

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".

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.

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.)

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.

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.

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.