If you found a used kid trailer for a cheap price, I'd say go for it. But Nashbar is offering their BoB trailer knockoff for $119 right now, which is really cheap for a purpose-built cargo trailer.

http://www.nashbar.com/bikes/Product...2_171082_-1___

I like the Xtrawheel idea, too. And the BoB trailer is great. BikeTrailerShop offerers a Greenspeed rack and adapter so you can mount a rack and panniers on the rear of the BoB trailer. I think you could carry your entire life on a LHT with front and rear panniers, and a BoB trailer with additional panniers!