I'm in the same boat, 8/3 10:30am to 8/12 6pm, so I'm 10 days you're 11. I have not seen any good downward moves for early August.
I've got a Standard (which shows as Emerald Aisle service) book with FlyingBlue and a $30 off coupon at $306.46 so your rate is probably the same with just one more day.
I experimented with Priceline - I lowballed on a full size, standard, and midsize. For the fullsize and standard, after my offer was rejected, I was offered an immediate opportunity to book at $15/day. I think I was offered a mid-size for $14/day. They don't show you the total with the fees until the next page - so for my 10-day rental, the $15/day came out to about $235. Still better than my $306 but I really like using National. So I'll probably try bidding a little bit closer to the trip to see if I can get in the sub $200 range. The last time I did Priceline, I did it too early.National ended up falling to what I got the Priceline Hertz car for and while the car was fine, I didn't care for the Hertz process. It took a lot longer than it does with National and I had an argument the Hertz agent on the kiosk screen tried to tell me that the Mustang he was going to put me in had 4 doors.
$70 is probably close to my threshold for guaranteeing a National car. I think I'd have to save at least $100 with Priceline to go that route.
I did have a really great experience with
Avis in California but I can't get anything close to a sane rate with them in Orlando for my dates.