At least in the next few days we should start seeing some coupons that go into 2014. A lot of the existing ones end on 12/31, which is today, of course.
A couple comments: March is still at least 2 months away, depending upon what part of the month you're going. I've gone the past several years sometime during March (but not Easter week) and each and every time the best rates were found anywhere from 2-14 days before departure. You can check every day, as an earlier poster mentioned, but in truth, its a little early for that.
I should give a disclaimer that my comments that follow apply to a common rental (MCO to MCO and one of the common car classes: economy, compact, midsize/intermediate, standard , full size/premium...of course, the terminology varies depending upon the agency). If you are renting in a class other than these, or doing a one-way rental, some of the "rules" don't hold, but here goes.
1. This far out, do not take a pre-paid rental. The rates may look good now, but if you look again 10 days before you leave, you'll be sorry. If you do take a pre-paid rental, do not look again.
2. The best rates are usually about 7-10 days before you leave. Starting at about three weeks out is when you should start looking every day. About then is when you'll see the price wars heat up and you may need to check several times a day. Car rates will change faster than airline fares.
3. Depending upon your situation, if you don't need a car for the whole time, you can rent (and/or drop off) from the Car Care Center or Swan/Dolphin (Alamo and National). There are also a couple agencies on Hotel Plaza Blvd (opposite Downtown Disney Marketplace). I forget the actual locations, but I think
Budget, Dollar and
Avis have locations there. Generally, renting from these locations is a little more expensive, but not always. Sometimes they're even less.
4. Despite everything I just said, it wouldn't hurt to make a non-binding reservation now. In all probability, you'll wind up cancelling it, but at least you have a safety net in case I'm completely wrong.
5. When you make a reservation that beats an old one, please cancel the old one.
6. Personally, my opinion is that you should be able to document any code that you use.
If you are renting one of the non-standard types (especially SUV and mini-van), the rules above may or may not hold. I'd still stay away from pre-pay for now.
A little history from last March. These were all for a weekly rental for March 8-13, 2013. The date you'll see is the date I made the reservation. First number is base rate, second is total.
12/14/12, Alamo, Compact, Disney Passholder/Entertainment free day: $207/$271
12/14/12,
Enterprise, Intermediate, Costco, $98/$143
12/17/12 Alamo, Compact, Costco/Entertainment free day $194/$255
12/17/12 Dollar, Intermediate, Dollar City Special, $99/$146
2/22/13 Alamo, Compact, Costco/Entertainment free day $148/$201
2/23/13 Alamo, Compact, Costco/Entertainment free day $132/$184
2/26/13 Budget, Compact, Costco/$40 off week coupon $135/$143
2/27/13 Alamo, Intermediate, Costco/Entertainment free day $89/$120
2/28/13 Alamo, Compact, Costco/Entertainment free day $87/$116
3/1/13 Alamo, Compact, Costco/Entertainment $20 off $84/$114
Other than a special from Enterprise and an early good Dollar City special, you can see the downward trend starting about 2 weeks out. The actual booking I used was the 3/1/13 Alamo compact, booked 7 days before departure. (Also note that once the rate gets down enough, a $xx off can be better than a free day)
And finally, here's my final booking for the three previous March's:
March 17-21 2012, Alamo, Compact $43/$78, Costco, booked 3/12/12, 5 days before departure
March 3-7 2011, Alamo, Standard $99/$144, Costco/Alamo promo, booked 2/18/11, 14 days before departure
March 20-24 2010, Alamo, Compact $73/$112, Costco/Alamo promo, booked 3/14/10, 6 days before departure