I have a flight credit that I want to convert to trip credit (and extend the expiration date). I am looking for the cheapest ticket that I can book using the flight credit, so the rest will be issued as a trip credit.

I found a $54 DEN-PHX one way flight. Is there anything cheaper than $54 (from anywhere to anywhere on any date)? Needs to be booked by 9/30/2022 for travel by 12/31/2022.

Thanks.