Anyone know tricks for getting good deals on larger rental vehicles?

DH and I are planning our next vehicle purchase, ideally before #2 arrives in June. We both currently have sedans and WOH with significant commutes. We don't want to go much bigger than we need on a day to day basis. We'd like to have more space for road trips and visitors but both are rare.

It would be ideal if we could rent something when we need it but we always find about $500/weekend. Way higher than renting a sedan. Plus the availability is quite limited.

Anybody have tips/tricks for rentals?