Sometimes your trans/t-case has to be in neutral to feel the play in the u-joints, if there is any. Sometimes you'll feel it all the time. Just depends on wear location and how the truck is sitting on the ground.
I looked up u-joints on RockAuto. Looks like you can get Spicers for $15 each... rebuilding your driveshaft is probably a LOT cheaper than a new one, they started at around $230. Make sure your slip yoke is in good shape, that would be the determining factor to me. Slop in that would lead me towards a new shaft.
Back in the day when I could find Bronco II's, I was occasionally using 91-94 Explorer front shafts to replace a Bronco II rear. There are some yoke modifications required on that route but it was cheap... a used driveshaft was like $10.