I imagine an elevator underwater, just below the surface.
It moves up 1 meter when the water level rises, by being slightly lighter than the water volume it displaces.
It moves down 1 meter when the water level decreases, and the mass of the object generates a greater force when it comes down.
By calculating the properties of the object, it could be engineered to stay at a certain depth.
I would dig a very deep hole, place a lot of objects calibrated for different depth ranges, like a vertebral column, and then use the force they generate when tide is lowering to generate electric current.
The generator could be on the surface, and it could be connected to several elevators like this, to minimize maintainance costs.
It could also act as a battery, when the elevator is high, the cable that connects it with the pulley system and with the generator could be stopped, and when energy is needed, it could be allowed to be lowered, resulting in a more consistent energy output.
It could be built entirely on land and just lowered into a hole, or dumped where the water is deep enough and it would settle by itself into place. The only things that needs installing are the pulley system and the generator, and if we're near the shore, those could be installed on land. If we're not near the shore, we would need a floating platform that would support the entire structure.
I'd just do the entire installation somewhere near the shore on land, and then dig a ditch from the sea to the elevator so that the water communicates with the hole I made for the instalation. This way I would still have the option to close the ditch and drain the well.