I'll be there for 2nd week in March. For some reason, rentals do appear to be higher. However, in the past, rental company specials have not come out until a month before my planned arrival. I got a really good deal for National with the Disney Club discount for a full size when I checked back in Nov. If I do the same request now, I get $100 more. Minivans were outrageous, but I finally found one with L & M that was decent. Through use of the codes and coupons noted on mousesavers.com, I was also able to get a decent minivan rate from Dollar, but it wasn't low enough to make me cancel my ressie with L&M. I ought to add my ability to get lower rates was from reading posts here.
If you've already checked mousesavers.com, then the only thing you can do is check and recheck every day. I should note that I have found lower prices as little as 48 hours before my arrival!!!!Though I've never used Priceline, a lot of people on this board seem to use it and enjoy it.
Good luck!
Sharon