I'd do the Poly/Synergy weld-in cage with the additions that Co4Lo did to his:
I currently have a River Raider weld-in cage. As a winter project, I plan to make some modifications to improve it, but if I were starting from scratch, I'd do the Poly/Synergy.
Spend $300 or so and do an evening welding class at your local College of Technology. It is worth it.
I just finished one a few weeks ago. It was about 3 hours of classroom time and 27 hours of lab time spread over 5 weeks. We did stick, mig, tig, aluminum, etc. It was a small class with only 7 students. So, a good percentage of the 27 hours lab time, I was directly tutored by the instructor.
A week or two after the class finished, I bought a Thermal Arc 181i (mig, stick, tig combo machine), and a Thermal Dynamics Cutmaster 42 plasma cutter. (Thermadyne is the company that makes Victor torches, Thermal Dynamic plasma cutters, and Thermal Arc welders.)
Next will be a tube bender and tube notcher.
After 27 hours welding, I am nowhere close to an expert, but I know how to make stuff stick together.
Anyway, that is my experience.