Originally Posted by
flyerCO
Only if the fare was the same is the change fee all that is charged. Now a lot of tickets you can change the return portion to a different date (not city) and as long as the same fare class is available and you meet any min/max stay restrictions, you only pay the change fee. However any other changes require a reprice to the current fare. Otherwise everyone would loads of tickets on a route when on sale and then simply pay a change fee to change the dates.
OP says that he cancelled a ticket and is now booking a new one. He is stuck with the basics of paying the new fare and $300 as a penalty for using the old value.