2004 Chrysler Sebring high RPMs and sometimes will not Move

I have a 2004 chrysler sebring and the car starts fine but on occassion when I put it into drive and press on the gas petal the car will not move. The RPMs go up and the engine revs but the car does not move. I have to press on the break and put it in park and then put it back into drive and sometimes I do this 3-4 times before the car will move forward. Once it is going it is fine for the most part. Sometimes it revs a little high on the highway or if I stop at a stop sign and have to go sometimes the same problem happens as when I originally started it where I press the gas and the car revs but just does not want to move. No engine light is on and I do not know if this is the engine or the transmission or what type of mechanic I should bring it to or how much it is going to cost me to fix.