If you want a good big metal one.. you could probably build one to be hacked pretty easy.
Find some metal... scavenge them if you can... Go look around builders square and I bet you cna find something. Get two flat pieces... one for the bottom, and one for the actual step.
get two hinges for the front.
get some fittings for the bottom to attach to your cabinet.
add two bars/flat metal on each side that stick out the top plate...and go into two cut slats in the cabinet. I would look for some T type fittings.. should be cheap.
Then on one side, have it trigger a leaf switch (if you want digital only)...
and the other side, have it attach to a spring. Either that, or a pillow, or something... something to push it up.
You might want to do the trigger on a 3rd pole in the middle and two on the sides with springs.