Square shaft might be the cost effective option... I am apprehensive about the square shaft though, I've read that they can bind under torque, won't let it extend or compress while in the throttle...
And can't they can be noisy while out of the throttle?
I want to get a doubler some day and that is when I plan on getting a real front shaft (HAD, Tom Woods, or the like), but for now I was planning on using a limiting strap.
The major factor I consider in every modification that I make is whether or not the truck will remain streetable. Square shaft would make a good trail spare though.