in essence your paying about 10% of the FULL FARE
and that is what an id90 is! But that does not include taxes which will add to the cost, so you end up paying 30% of full fare for a standby ticket, seems reasonable to me.
I just paid HKD3400 for a business seat on Delta, which was around a 1/3rd of the full fare ey ticket, sounds reasonable to me.