There is also this option: http://www.xtracycle.com/cargo-bicyc...o-bicycle.html

I often think about adding an Xtracycle to my Kona Smoke. A whole lot cheaper, without too many downsides. Oh, but where would I put it? The only bike-free spot left in my tiny apartment is the bathtub.

So far I haven't heard anyone say they wish they hadn't added an Xtracycle to their bike, nor say they regret buying their Big Dummy.