actually 300$ isnt that much if you take in account that business tickets on this routing is usually arround 6000 - 11000$ (without taxes) and a ticket that is discounted down to 3000$ has some restrictions which means in that case for the z fare a few days advanced pruchase (for rebookings) and a min and max stay at target destination, and also a penalty for cancellation and/or rebooking but that sounds fair to me.
i personally think that 300$ isnt that much at all to cancel a ticket that is discounted down that far.