1280x720 is HD
1920x1080 is Full HD
3840x2160 is 4k

Interesting.

H.D. monitors are reasonable in price, but the graphics cards are at least $450.

I don't have graphics cards, just i5 in my laptop and one in the desktop. Haven't hit a snag on HD video or games yet.

Edit: but am not a big gamer these days, last games (PC) were: The Matrix: Path of Neo, CoD4 and Doom 3... I know there are likely games I'd need upgrades for, wtv. Movies can always just reformat if ever comes that time...

No..not even close

You don't even need a graphics card to run anything at that low of a resolution

"high definition" is anything above DVD (480 pixels vertically).

And all CPUs can do 1080p without GPU assistance.

I like to use mediainfo. It's a cli tool, but has a gui too.

There are also cheap graphics cards well below $450 that display 1920x1080.

I bet many gamers (&c) like upgrading them regularly so could probably find a lot of good used ones...