Funny, I was just getting ready to post something similar!
I am just sick. We booked early to ensure a cheap rate. I was just checking the site tonight and noticed our same dates went down $ 20 per leg of the flight! There are 7 of us going so....total of $ 280 round trip. I looked at the web site and it says no credit will be given if the fare changes.
I am sick too! Don't know if we could press the issue with them or not. I think a $50 per ticket applies for cancelling.
According to Allegiant's FAQ http://allegiantair.com/aaFAQ.php, no, they will not credit or refund any fare difference
"What if the fare drops on a ticket after I have already purchased it?
The desire for the lowest possible fare is understandable; however, Allegiant Air unfortunately cannot refund or credit fare differences after a reservation has been made. When the original ticket is purchased, via the web or by a reservations agent, the purchaser of the ticket is prompted or asked if they agree to the following terms and conditions in order to purchase the ticket: "All tickets are non-refundable, one-way, and ticketless". This is because Allegiant Air unfortunately cannot control when a passenger will book their flight. Allegiant also does not have advance knowledge of when specials will be offered. The fluctuation in a fare may also be caused by cancellations, and since Allegiant does not overbook its flights, a seat may become available at a lower price."
As for cancelling (and rebooking at the lower fare, I guess), the same page states "Please refer to the Reminders and Fare Rules portion of your confirmation. "