Hi Geoff,
Check out http://www.wike.ca they are an internet only bicycle trailer company out of Guelph Ontario. They have some nice simple no-weld cargo trailer kits (along with an array of pre-built trailers). Not the cheapest but very good quality and service. They are also open to negotiating bulk purchases of their hitches, tube joints and wheels. I personally purchased their cargo kit and their canoe trailer and have been very happy. Buy the metal tubing and good quality nuts & bolts locally in bulk and I'm guessing you could get the costs down to the $100-$150 range.
Chris Wells
(Email Handler & one of many Volunteer Head Mechanics & former resident of Winnipeg) 

re-Cycles Bicycle Co-op
473 Bronson Ave. Ottawa

From: Geoff Heath <mech@thewrench.ca>
To: thethinktank@lists.bikecollectives.org
Sent: Fri, March 18, 2011 12:04:49 PM
Subject: [TheThinkTank] Bike Trailer & teaching skills workshops

Hey folks
Geoff from Bike Dump & The WRENCH up here in Winnipeg.

We're organizing a summer workshop series and 2 of the requested topics are trailers and teaching skills for in the shop.  So I was wondering if anyone had done workshops on these topics and could share their materials/experience.

Is it even really feasible to do a trailer workshop in one day given that most designs involve substantial cutting, welding, etc?

Also, does anyone have notes from the "HOW TO TEACH HANDS OFF"  Workshop at last year's Bikebike?  it ain't up on the wiki sadly.