skymeat the frame itself weighs nothing much at all, i was lucky enough to have a spot for my rig that didn't require it to be packed away, but all up including the seat , wheel and frame i'd say mine weighs 30 to 35 kg, and if you can infact weld and/or have a mate that can help i'd recommend using steel, the open part of the rig i just went out and tested and i sat all my 80kgs of fat ass on it without any problem, he's a part of the article i wrote explaining the difference in materials.
Copied from my 95% completed instructional.
" Whether to build out of timber, steel or aluminium was an interesting problem, timber was easy to assemble but had weak structural characteristics, steel on the other hand had great strength, but with the lack of welding skills it was not going to be easy to assemble, where as aluminium had both strength and ease in assembly but it was going to cost me more than what my real car was worth.
So I made the logical decision and found myself a friend that could weld. Although I could do all the cuts and lay out all that was needed, my welding was not a strong point and that’s where my mate came in handy, so here is how I got to where I am now, I cant give advice on how to weld, so you'll have to find yourself a mate like I did, or build it out of timber and put extra structural supports in where needed which is totally do-able. So here are the plans and just a guide to what I did, and any issues I encountered. "
btw, the frame cost me 32 aussie dollars in material, and i just bought it from a steel place, so very cheap