You can always try Priceline. They have their best car rental rates usually 10 days to 2 weeks before pick up so you are right in that window. I would look at various conventional booking sites and at mousesaves.com and look for coupons, etc and see what the best rate you can get via a conventional booking is and then try a Pricline bid for about 30 to 40% less than the best daily rate you can find (remember the taxes and fees on Priceline for rental cars is high so be sure you are comparing the bottom line (after taxes and fees are added) to the final cost of a conventional booking. Then if you cannot get a decent rate on Priceline you are not out anything and you can go with the conventional booking.
Typically you get the best Priceline car rental rates on shorter stays like yours....often if you need a car for a week or longer you can do as well or better with a conventional booking.