Most exhaust is mild steel stock, I'm sorry but I've no idea the wall thickness - me and numbers lol
However - mild steel of that size is fairly simple to bend yourself. Any two points of contact and leverage will do it, best if you can find a round surface - but just about anything will do. People 'round here have used conduit with success - I've just not messed w/it myself.
Lotsa lil bends to make a big or sharp bend, that's all there really is to it if you haven't a proper tubing bender. If yer going with stainless tho it's another matter - that stuff is rugged and somewhat brittle/prone to cracking from bending abuse. I personally think stainless is great - but maybe not worth it for the do-it-yerself... maybe not for this application either - I'd just make another if I needed to. It's all up to the builder tho
I'd still go with a tuned exhaust, even a custom job - over a regular pipe & can. It's just too much a response to overlook - the 2 stroke begs for 'em lol
The two springs on the SBP's pipe are because it's a flexible joint. Common to see on other "small" 2 stroke vehicles like snowmobiles and ultralights, it helps reduce metal fatigue due to vibration and torque flex. It is
usually a ball & socket joint, the SBP's one also gives more options for mounting orientation.
There's a buncha sweet expansion chambers out there and a few different styles, I do favor the SBP one obviously