[antony96 (OP)]

Do rare earth metals get used in alloys? Given their high price, I’d assume not.

[wolfekeeper]

Yup, they're used for specialist purposes, many of which are exotic and very expensive, but you've very probably got some around your house. Neodymium magnets are alloys of neodymium, iron and boron and others.

[Bored chemist]

The "rare earth" metals are commonly used in alloys- not least because purifying them is difficult and, for some things, pointless.
They are expensive, but not as expensive as they were.
https://www.businessinsider.com.au/molycorp-decline-in-2014-2014-9
and they are, for example a lot cheaper than silver.
If I'm reading this right then cerium (as the oxide) is about 20 times cheaper than cobalt.
https://www.lme.com/en-GB/Metals/Minor-metals/Cobalt#tabIndex=0

https://www.statista.com/statistics/450146/global-reo-cerium-oxide-price-forecast/

[wolfekeeper]

Apart from supermagnets, another extremely common use for a rare earth alloy is in lighters:

https://en.wikipedia.org/wiki/Mischmetal

"Rare earth elements" are a bit of a misnomer, they're not actually that rare. In the UK, there's potentially commericial deposits in Wales. The real problem is the purification step, it tends to produce very toxic chemicals. But still, rare earth elements are usually not super-duper expensive.

[evan_au]

See: https://en.wikipedia.org/wiki/Rare-earth_element#Uses

I work in telecommunications, and Erbium-doped optical amplifiers are used to amplify the laser signals that carry the internet around the world.