Eth2's design supports staking pools though, so it just takes ~$20 to participate, depending on the pool. Granted, some of the staking rewards go to the node operator, but it's a competitive market, so the difference should be comparable to the costs of operating a node.

There are also some sharded PoS designs where staking can be done in a really lightweight manner -- the process can be mostly idle, and only sync when it's the user's turn to do something -- even on a mobile device.