Good rate!

I went to look on my dates in November and it's $40 cheaper than what I've booked through National Emerald. But since it was Alamo, I don't understand how it could be $40 cheaper, aren't they the same car rental company? Anyway, I might make the change when I get closer to the date. But I booked with a free additional driver code, so maybe it's not that much cheaper... I hate to be DD for my birthday celebrations!