it's only 160 RMB, which is... less than $30CDN. it's cheaper than the CN tower.160 bucks for a ticket... man...
it's an expo, not some sporting event where there are a limited number of seats available. the area is huge and it lasts for 5 months, so i doubt the tickets can be sold out at all. In fact, i don't think there is a set limit on how many tickets can be sold in total.