Well, if you eat the sachima right away, then it is ok. However, since it is already pretty hard, any small amount of drying out will make it way too hard in my opinion.
"But I guess the tourists may buy 2, instead of e.g. 4 "
That is fine. Golden Gate is always selling out their egg tarts and I would say that people are more discouraged by the long line instead of the price point.
Good quality stuffs deserve a good price. In my opinion, if a boring Starbuck pumpkin scone can be charged $3 (and they expect you to tip them too), I think $2-3 good quality egg tart is well deserved. Starbuck pastries are not out of the world…
