I would hit the airline websites and go from there. United was advertising $199 Ea Way from San Jose,CA to all destinations in Europe last week. So cheap flights are out there without using Priceline or Hotwire.com. Orbitz, Travelocity, Expedia use Airline Web sites rates and sometimes charge extra for processing fees.
If you don't care about flight times, layovers or the like Priceline is a good choice.