I just noticed this too today when comparing rental car prices. I thought, "Wow, priceline actually has a cheaper rate directly than what AutoSlash has, let me read the fine print!". Of course, the "cheaper" rate I was seeing was their non-cancelable, expressdeal price... I'm glad I looked!

Autoslash still has the best rates I can find that are fully cancelable, without any hoops to jump through besides, sometimes, the 48-hours before pickup stipulation.