Two one way tickets from a major airline is really expensive too. Your best bet is to look at an airline such as Jet Blue or Airtran, which don't charge you extra for a one way ticket.
For me to fly from LA to Rochester (NY), It's often $300-350 round trip with American or United (the places I have frequent flyer miles with). However, a 1 way ticket for the same date is often $400. With Jet Blue, a 1 way ticket is often $200 or less.
And priceline is absolutely the wrong place to look for a ticket if you don't know a return date.