Help with the front axle...

As I'm relatively new to the wheeling thing, I've never had a front axle pulled apart. Look like it's something I'll be tackling pretty soon, though. A few thousand miles ago, I began to feel a fairly pronounced vibration in the wheel, it's obvious that it's resonating at wheel speed. There's now a good thump when driving around slowly - and after having a rock tap in time with the thump, I have to assume the problem I'm having is somewhere between the axle and tire.
I'd initially thought it may be my tires - maybe a broken belt or tread separation, but after an inspection and balance, they got a clean bill of health (33x12.5 BFG MT/R's with around 18k on them).
I swapped a rear 44 in to my old Jeep, but that seems like a much less daunting task than fumbling around with the front end. I've always been a bit wigged out screwing with the steering on my vehicles, but I suppose I'll get over it.
Is it likely the stub shaft is bent? It doesn't make sense to me, but is it possible that a bad bearing could cause the low-speed thump/high speed vibration?
I'm hoping there's a fairly quick, cheap solution as I hadn't intended on keeping the 30 under the Jeep much longer - at this point only until I feel it's safe to spend the money on some beefy axles.

Sounds like the front axle U-joint, if it's really shot, a flashlight and an inspection will show obvious slop in the end caps. Something you want to take care of before the wobble in the shaft screws up the differential oil seals.
There has been many write ups on swapping out the U-joint, a pain, but doable by most with moderate abilities.
It's likely something you'd want to do yourself anyway, at least once in the driveway. So you'll have some practice for if or when it messes up someplace away from home and far from a gas station.

I second what 8Mud has said.