This topic has been hashed out before. The general conclusion was that due to infrastructure and overhead costs, (training, updates, WC, benes, etc) many facilities seem to prefer agency and travelers in many situations....so it must make fiscal sense for them to do so.
Agency nurses prefer to NOT be under the thumb of the hospital, so the agencies make $$$ off this fact.
I'd like to see ALL of us go independent myself and stop giving our power away..
In my area agencies charge about 1 1/2 x the nurse rate, but this can vary.