i'm just finishing up a senior design project that fell well short of being completed. I've been stressed out all school year and all i want to do is relax and coast.
keep it simple. Making an E-50 case is hella difficult, and you're still stuck with figuring out the whole variator thing, because scoot cylinders are mega hi-rpm and wont work well with one gear.
you wont get it to market for $400 unless you plan on doing all the work yourself and paying yourself nothing. The casting alone will be close to 100 because of all the cores required.
keep its simple, do something cast iron that doesn't require $200 worth of plating, or machining of a sleeve and all that nonsense.
the statistic i heard for mechanical components is, the final cost of a product is about 4x what it costs to strictly manufacture. There is a reason nobody stateside has been able to get any moped parts made by casting. its pretty hard, the process is very time consuming, and even if you know what you are doing there is a pretty good chance you'll screw up one or 3 times.
check out josh's nerdspeed blog, he tried to cast a cylinder a few years ago, and has some good info on the process.