Glad I clicked this thread. I tried autoslash and improved two Costco auto rental bookings by quite a bit. One booking changed from Dollar to Hertz and the other from Alamo to Dollar. Both at reduced rates through priceline. If the free extra driver is important to you, stick with Costco but they are not always the cheapest.

I like the autoslash promise to monitor for lower rates.

Jim (not a shill )