With a little effort you can make a durable and reasonably light weight bicycle cargo trailer, from an existing kid carriage, such as one discarded because the fabric is weathered or destroyed. These are easy to find in scrap-yards, through 2nd hand stores, garage sales, and classifieds.
I made my trailer for under 20 bucks. I had to buy a couple cans of paint, a sheet of sandpaper, a spring for the hitch, and a replacement bolt & knob for the hitch. I already had some wire panel. Those are about $15 each, so you should be able to build this trailer for under $100 easily, even if you need a replacement hitch or something. I'm going to add a reflective sign or panel on the back for going can collecting and fishing.
I suggest a steel frame trailer with 16 or 20" wheels, quick-detach wheels, quick-clamp hitch, and folding capability. The Safety First model is easy to find for less than $50 even in good condition. I got one from the trash for free!
UPDATE: This trailer is still in use, and working well. The rubber/plastidip on the clamp has come off, so I carefully padded the clamp with Gorilla Tape. This held up all day in 100+F heat, and did not scratch the bike frame. Make sure the corners of the clamp are protected or they will 'bite" the frame.
Step 1: what you will need
1.You will need a Safety First cargo trailer, or similar model.
2. Wire "hog panel" from feed store or hardware store (about $15 each, will have enough for 2 or more trailers)
3. Probably a set of tires and/or heavy duty tubes, I suggest www.niagaracycle.com for budget replacements
4. Possibly a replacement hitch or parts. I will discuss that more in this article
A. Need a hacksaw, or bolt cutters, or a cutoff saw, to remove unneeded metal from trailer, and cut wire panel. I used a hacksaw, but it was slow.
B. Vice Grip pliers, to bend the wires on the panel
C. Appropriate screw drivers, allen wrenches, or wrenches as needed to remove buttons, reflectors (save them), etc while removing the fabric and seat. A sharp knife and/or box cutter can help in removing the fabric parts.
D. measuring tape and a Magic Marker/Sharpie
E. A small crescent wrench or two, to remove the pivot bolts from the side hoops of the frame (keep the hardware and hoops) F. 60 grit sandpaper, to remove rust and old paint or chrome. If it is chromed and not in bad shape, you might want to leave it that way. To paint over chrome, scuff the surface up to take primer.
6. Paint and reflective devices
Note: if you don't want to mess with paint, or live in an apartment, you can buy colored Duct Tape, even in camouflage patterns!
A. 1 can of black or red/brown primer. 1 can of each color you wish to use. I used Krylon Ruddy Brown Primer and Krylon Satin Hunter Green paint. I highly recommend the specialty Krylon camo coordinated primer+paint combo colors, about $5-7 a can. they are non-reflective, and very durable. I painted a car once with them. It lasted for years (the paint).
B. Reflectors (sometimes they come on the wheels and trailer. Save them if you can. You can obtain them from bicycle shops, junkyards, scrapyards, usually in take-off bins or on old kids bikes. You can use rubber shims to make them fit the tubes on the frame, or epoxy them. You can find a million free pedal reflectors in white and yellow colors, along bicycle trails in the woods. haha They fall off of cheap pedals. You can tape or glue them on.
I suggest Reflective Tape from trailer accessories depts at auto parts or hardware/ag stores. This can be wrapped around any tube and will shine brightly when hit with lights.
C. Flags, reflective panels, blinking lights, or extension wands. Bike trailers often come with flags and poles, usually an orange triangle flag. This is cool, and replacements are cheap. You can make one from a piece of PVC pipe or broom handle, and attaching a flag you like (such as your country or state flag, or an orange warning flag. These help especially in hilly areas. I highly recommend battery powered red blinkers and white headlights, on the trailer as well as your bike. Dealtime Extreme, Lazerpoint, Amazon and bulk battery stores have them straight from China and Taiwan for $2-5 each, like this http://www.lazerpoint.com/p-5-led-6-mode-multifunction-bicycle-taillight-with-bracket_7945414 You can make extension warning wands (to discourage close passes) by zip-tying a foam pool toy ("noodle") onto the rear bumper bar of the trailer, or to your bike's rear rack.
7. Baskets and cargo bins, rope, and straps.
A. I highly recommend common laundry baskets, milk crates, and discarded picnic coolers. You can tie them to the trailer frame or wire grid with climbing rope, clothesline rope, or motorcycle straps (cheap cargo straps are available in the "king tools" bargain bins at hardware stores, in the big stores such as Big Lots or Harbor Freight, and Walmart.
You can bolt down picnic coolers or Action Packer boxes with j-hook bolts, washer and nut combos.