It's doubtful they'd match it. And you are still 6 months away, even if they did price matching, they wouldn't do it this far out IMHO.
I can tell you I was originally going to do with Dollar for a minivan my last trip, but I ended up with National. Dollar's total price was about $40 less when I originally made the ressie. I much prefer National being an EC member as well. Well, about 6 weeks out, National's prices dropped and beat the price I had with Dollar by about $7.
Now adding in Emerald Club benefits like walking straight to the car and no extra charge for spouse as an extra driver, I of course took National.
The other thing that bothers me with Dollar is that they only guarantee base model minivans (ie Caravan - not Grand Caravan) and you can only upgrade to a long base minivan at the counter and IF they have one available. When I checked at National, there were several Grand Caravan, Montanas and other minivans with the longer wheelbase which gives you more room for luggage. We had 6 people's worth of luggage for a week's stay - I needed to know I would have that extra room.
So keep watching National and I think as you get much closer to your travel dates you will find the rates a little lower.