Gotta be honest, I wouldn't try this option even if the boxes were free. I don't wish to be overly negative about things, but China is not the place one normally assosciates with quality control and the like. The fact is thigs are made cheaply thee. No employee is going to give a damn when they earn a few dollars a day.
This is a difficult process (imho gear manufacturing/machining/hardening is about the hardest mechanically based sub section of auto manufacturing) and there's a reason that Albins Gears
http://www.albinsgear.com.au/ charge what they do (and if the actual costs of developing an alternate ratio set for any new gearbox with relatively limited sales potential, they aren't pocketing much profit at all), and furthermore that there's no shortage of racers who do business with them. It requires massive knowledge, expensive machinery, the best raw materials and significant experience to do it right