I would if I were you, you are just lucky you have fallen on a good rate for the car you want on your dates.
I am looking for
7 seater 5th-19th August
Full size 19th-28th August
Hertz want £1040.18 (1 driver for each car & no fuel)
USrentacar £656 for both multiple drivers and a tank of gas in each.
All booked, I think you are right. Some of the other companies were asking silly prices though, I went through the amex offer with card holder benefits and they wanted £500 odd for the same thing!
I hope that you manage to find a good rate in the end.
I am just in the process of booking with USrentacar, will pay the extra £16.42 which allows me to cancel them both if I see a better rate. Better get it done and to bed, another early start tomorrow.