Here is the OEM of the bed lifts mentioned earlier:
Other commercial possibilities are the lift mechanism for a popup top camper or popup truck camper:
RV parts are usually quite inexpensive, so if can figure out how to buy these parts wholesale, my guess is that it would rival the cost of buying the individual pieces and trying to build your own mechanism.
Basic linear actuators are affordable. Getting them to move in sync adds quite a bit of expense. You need to add a position sensor (typically "hall effect") and a box that monitors the positions and keeps them in sync.
I would avoid a scissor lift if possible. There is a tremendous amount of lift force wasted at the bottom of the stroke pushing sideways rather than up, so it starts at a mechanical disadvantage. There aren't any off the shelf mechanisms. You'll have to figure out a way to keep your stuff clear of the mechanism.
As mentioned earlier, if you build a lightweight bed platform, you could move it up and down manually.