If you have to pay a welder I doubt you'd build one cheaper than that. Welding with a mig is fairly easy to learn and fun to do. Your chances of cutting all the bits perfectly to be able to weld it all in one go are slim to be polite about it. Aligning the various parts easily takes as long as welding them. It's much easier to cut and weld as you make the individual parts or sub assemblies which also makes employing a welder much more expensive.But to get a trike around here forget it, your not touching one for under $800 used!
Brazing is plenty strong enough in a lugged style joint. The plans use butted joints which require welding. You could modify the designs to utilise lug joints but to make them you'd need a welder anyway making the whole process pointless. Bamboo is immensely strong and more to the point has a certain give to it like steel does. It's kind of like natures carbon fibre but with the benefit of being usable in beam positions too unlike carbon fibre as it has that give. Modern glues are good enough to hold various car chassis together such as the Lotus Elise and are proven stronger than welding. Again though not suitable for a butt joint.so brazing is not strong enough but bamboo and two part epoxy is
I think that one has bad press for it's steering geometry etcLast chance
Alloy bolt together trike