I haven't built it yet so take this with a block of salt but here's what I will be using for my Penthouse lift.
400 lb Force 30" Stroke
In my case it will be a permanent mount but I don't think it would be too difficult to take one of these actuators and add a base, top plate, switch, plug and fuse onto a portable style. Especially a fuse. The actuator is $116 so with the other parts it should be done under $200.
The one thing I haven't figured out yet is how big the top plate would have to be to spread the force out so it doesn't punch through the roof.