For some reason I can't pull the blog post up, but I've been looking for something similar also. I thought about a harbor freight trailer also because I thought I could move it by hand on level ground. HF also sells a trailer dollie with a ball for about $60 that would make it easier to roll around.
I've also considered building an egg mobile out of an old wagon which can be bought around here on craigslist for $400-$600 for a decent piece. This way, there would be plenty of room for
feed, rain
water collection, electric
fence box/battery, and for them to stretch their legs when it's too nasty to go out(which doesn't happen often, but it does happen here). The only drawback would be that you'd have to have a truck,
tractor, or
UTV to move it.