I think this is the pell that Jake is talking about
http://www.karateconnection.com/dummy.htm really strong design, it'll probably last a lifetime.
I made my portable pell for around $15-$20 and so far I'm really pretty satisfied with it. I took a 2' x 4' piece of 1/2" plywood and attached a 2" galvanized floor flange to it. The flange was placed in the middle of one of the 4' sides (this gives you 2' of bracing at the rear and 3' to either side). I then screwed a 12" long piece of 2" galvanized steel pipe into the flange. I made the striking surface of the pell from a piece of ABS plastic pipe (I used a pipe diameter that was just big enough to fit
inside the 2" galvanized pipe. I covered my striking suface with several layers of carpet with extra layers at approximately shoulder and hip height and several extra pieces on the top for reinforcement. This is all covered in duct tape. It can easily withstand the hardest blows and is light and extremely portable. The only downside is that thrusting straight on tends to knock it over, however if you move so that you are thrusting with one of the longer sides as the brace, it won't fall over.
Cheap and easy. I don't have a picture of it available right now, but can take one for anyone who is interested.