At the local sports store in the gym equipment area is a device for this too.

It's basically a frame that's constructed to do chin-ups on. Free standing... and adjustable. Best of all, it can be put up and taken down in a few minutes. I'm about 6 ft, and bar was high enough that I had to stretch to wrap my fingers around.

Another device that's foldable and portable is something used in garages called an engine hoist. I'm not sure how high you can raise the arm with the jack, but know from experience you can use one to hoist a fairly large sub with that's laying prone.