Scrap convertible cars can often be found cheap, and contain a full hydraulic system which may hackable for machine building. I am trying to find information about the force deliverable by these actuators. They have a reasonable stroke length and could be used in pairs or sets of 4.
Also looking into hydraulic rams from tipper trucks which can be found cheap; come with their own pump, have a long stroke and might be powerful enough to be use individually. I thought about forklift rams but these often run on a shared hydraulic system so I’d need a separate pump. But that would be one hell of a stroke, a very long barrelled machine!