I've been thinking of getting on of these myself and although there are a lot of larger pricey models out there, you can also find some resonably priced ones not too much bigger than your adverage breadmaker.

I haven't made a purchase tho as it seems relativly easy to build one yourself. There are several lots of plans on the net and if you have the 'preserved' book there are some in there too. I think in the end building one is the way I'll go cause you can make them big!!!

Now if you'll excuse me I have to get back to my plans to build a veggie watering robot that will eventually take over the world and force everyone to grow their own!!!