I found a piston elevator in one of my snapshot worlds, and it didn't really work well, so I asked a friend for help and we made this extremely simple (and easily expandable) piston elevator design.

It's also really simple to build, here's how it works:

There is a moved block pulse limiter at the bottom (see image below) which connects to a tower of inverting redstone torches and pistons spaced two blocks apart. Its really simple to build once you get the hang of it, super cheap (no slime blocks!) and infinitely expandable.

(Also, if anyone finds a cheaper one or needs help understanding this one, just let me know )