There's really no secret. I prefer using the priceline view so you can see them all side by side rather than in a list. One option is to use transfercarus.com. Sometimes they have great deals when the rental car companies need to move cars from one location to the other.
One thing to consider is it will likely be cheaper to book a one-way rental for only one day and then return the car and pickup another one for your time there since one-ways daily rates are often priced higher.
You could also try priceline's bidding service and hotwire's opaque booking.