We had a straight key building competition at one club meeting
many years ago. One design was built from Lego blocks. One
used a large tarnished serving spoon. Another used a pink
toy "squeaky" bear, with the squeaker removed and replaced
with a plastic tube that inflated a balloon to operate a microswitch
when the bear's tummy was pressed. There were others.
Most actually worked reasonably well at 20 WPM - even the bear.
So not only can keys be easy to build, but they can be creative, too.