You can get into it for a reasonable price by using the 3lb rock tumbler that
Harbor Freight sells. Does smaller loads (25 450b or less) than the nice $269 Thumlers unit. I run my decapping stem out far enough to not begin sizing the case, pop out the primers and throw the cases into the tumbler. For that smaller tumbler I use a 9mm empty case of LemiShine and 2-3 drops of Dawn. In the summer, I run a dehumidifier in the shop with a 1-1/2 gallon hopper which thanks to our wet spring, still gets filled every 24 hrs. I use the water it removes from the air for tumbling, but tap water works as well. If you watch the HF sales, you can get that tumbler for $29.95. I still use my vibratory tumbler for removing sizing lube, but that's about all. That having been said. The first 2k 450b cases I processed were through my vibratory tumbler and walnut media (also available from HF). That worked fine as well. Just required cleaning the primer pockets manually. Performance wise, I haven't seen a benefit from the wet tumbling, but it's result is very pleasing to the eye.
Hoot
EDIT: HF has the dual drum (50 450b cases) version of the tumbler on sale for $54.99 right now.
http://www.harborfreight.com/dual-drum-rotary-rock-tumbler-67632.html