Building your own trailer should be easy on the pocket, making use of easy to come by bits. There are a fair few sites offering instructions on how to build your own bike trailer, often out of reused bike parts and sometimes needing no welding.
DIY Longtail (Xtracycle style)
Another diy project that needs no welding – this time a longtail cargo bike.
In 2013, two of us cycled to The Gambia from northern Spain to work on a bicycle recycling project. We created a similar longtail cargo bike, as seen below. This one, however, was welded.
The full article relating to the building of this cargo bike can be found here>>
Another cargo bike built in the Gambia, this time in a Long John style can be found here at Atomic Zombie
And here’s the video of it being built.