Bait and Switch laws say no.

They cannot show you one price and then at checkout charge you something different.
(Sales tax excluded of course)

This is also to prevent people from abusing the price differences to get their buddies to get them games for cheaper than what they are supposed to be paying for.

引用自 Ben2tu：

I understand that there is a price difference, in this case, why can't Value adds a special gift rule where if the person is not in the same region as you, you need to automatically pay the highest converted price in their local currency.

Because Valve is not allowed to just charge you a different price than what you were shown. YOUR price is YOUR price. You should not ever be made to pay more just because of "reasons".

引用自 Ben2tu：

Otherwise I have to change my region but it's absurd to do that considered that I live in China.

You are not supposed to disguise your location so that you can buy games at different prices. That's an SSA violation. Send your friend a Digital Gift Card and tell them it's for them to buy whatever game you want them to own.

Every time someone comes up with an "obvious" solution to a problem I wonder why they don't think about why Valve didn't do the very "obvious" thing being suggested.