yungfourfour

It really depends, the bottom line is to give the "cost" for dinner + "wine water costs" in dinner la

If your friend is close to you, you can pay more
If you know both of them work really hard (financially) to get to this stage, by all means pay decent

but let's say if both of them are doing well and they have rich parents, a special gift instead of "yun ching" is still acceptable.