Here are some pics of a cheap home built trailer for use with a bike or trike. I made it from a walker and some bits from a second walker. It is currently set up with a hitch mounted to a rear rack but I have left an arm on the left front of the trailer to accept a conventional bike trailer hitch which would mount to the drop outs.
http://picasaweb.google.com/tjdale2/Hom ... keTrailer#