Car rental rates double a week or two prior to Thanksgiving and then rates triple after Thanksgiving & through the holidays. You may want to reserve what you need and then continue your search for a better deal.
One option is to reserve a vehicle at one of the places close to DW instead of at the airport. We are taking a taxi to our hotel on the 23rd and then will pick up our car the next morning. When we depart, we can drop off the car at the airport and there aren't any additional costs to do this. So, we will only have to pay for a taxi for our initial trip to the hotel. We are saving about $400-500 (because of current rental rates & no airport fees) by doing this.