Sept. minivan rates?

[shelly3girls]

I need to rent a minivan for our Sept/Oct trip which is a total of 5 days. It has to be a larger minivan that seats eight since we will have 3 adults and 4 children plus luggage. I have checked around and the cheapest I can find is Alamo using the Walmart code ($260 + tax = $314) with National being about $20 more. Is there a way to get a better rate or do I need to wait until this summer and hope some discounts/coupons are released?