FedEx and Uhaul sell boxes for reasonable prices. FedEx has a two piece telescoping box that will probably work. Scroll down about half way in this link:
I had one made as well, found a bent station wagon driveshaft and had it re-tubed. A mopar buddy of mine worked at a drivetrain shop needed a truck tranny. I had one laying around so we swapped. I paid 20 bucks for the driveshaft at the junkyard, so total cost out of pocket, 20 bucks.