I have done a few transactions on Alibaba and I would be surprised if the total cost of er9 is less than $500 to your door if you live in a western country. Its often cheaper to buy things on Aliexpress simply because sellers on Alibaba are passing all the fees on to you. A recent purchase of 50 garmin inserts for example was $20 cheaper on Aliexpress than Alibaba from the same seller.
Given that my target price for batteries, RD, FD, and shifters/brakes for Rival AXS is ~$700, I dont think I am in the market for er9 or ERX either given that warranty support is important for groupsets.