I'd disagree Priceline is always useless. I got sme very good rates for 7 and 14 day rental at LIH last month. Cheapest rate I could find (tax-inc.) for a minivan was $518 for 2 weeks from National (checked all the majors with all the coupons/rates I had at my disposal). PL gave it to me at $331 all-inclusive (@$18/day), and from National too! Around the same time, I also got a convertible for 7 days for $170 all.inc. (also $18/day) also from National while the cheapest I could get was $300 elsewhere. All were accepted first bid so perhaps I paid too much!

You just have to research (yes, it does suck up time) and then submit a bid at PL for at least 40% below the lowest you found to account for fees/loss of miles. I have gotten really cheap rates direct from the car companies that PL bids couldn't match (e.g., 6-day in FLL @8 for an "economy" Neon), and pretty good 4-day Minivan rates at Alamo in HNL and KOA that PL couldn't beat.