Hi Timberwolf and welcome to the forum.
There loads of info on the web as well as here, have a search and see what you come up with. I made one from industrial air hose, nylon rod and some turned aluminium. It worked well for quite a while but I've left the seals inside the cylinder and they now leak, so a bit of repair work is needed.
Once you can see how simple they can be, you can make your own with supprisingly few tools, though the technique may take a while to learn.
ATB
Ogri the trog