I have a reservation for the week before April (4/8-4/15). I tried Andy's, Marshall's, Expedia, Orbitz, and National with my corporate discount. (To my dismay, Costco doesn't even rent on GC.) The cheapest I was able to find was via AARP's travel site. (We're 50 now.) Ended up selecting a mid-size SUV. We could probably fit in an intermediate car, but I prefer SUVs because I get car sick.
Price was ~$420 for the week, which we'll split with another couple. FYI, all drivers have to buy a temporary driver's permit that'll set you back $20 each.
If you don't belong to AARP, I believe they use the same travel provider as Entertainment. I know they just had a big sale ($19 for every book) over Thanksgiving. Might be worth a shot.