PrePaying Alamo Deals

[DisneyMomJen]

We will be in Disney August 25th - September 7th, 13 days, needing a mini-van. I have been checking and the lowest prices I was getting were close to $600. Well, last night I checked Alamo which was coming up for $471, prepaying and $20 entertainment coupon. I checked again when I was ready to book and it was $448. So, I booked thinking this is a GREAT deal! I check this morning and it is $434. There is a $10 cancellation fee.
Does anyone have any experience with this and do you think the prices will keep falling?