They're not really rare. For example, here in Brazil, it's just a common thing in houses to have an old crt lying around, sometimes, still in use. People sell them for really cheap, or just give them away (since they're heavy, a lot of people will gladly give you one, or two, for free if you simply go there to take it). Even in a country where crts are rare, a collector could simply import one from a place where it costs almost nothing.

Crts may be old, but they were manufactured in millions, making them not really valuable, because they're not rare. Same goes for things like floppy disks or coins from periods of huge inflation. It will take a loooong time until we see crt prices skyrocketing due to scarcity. Prices may have gone up a little in some places, but not that much.

As for the shrek one, like people said, it's because it was a limited model.