1993 Ford Probe Shifting gears and getting up to speed

I just bought this car from a friend it runs fine in every way except today I began to have a problem with the car getting up to speed and a high revving when in gear. My car is not shifting correctly and is revving extremely high without getting much speed. For example, when I go from stop to first the motor revs around a 6-7 on the RPM gauge but doesn't go above 10 MPH shifting into second gets me up to 25 MPH and Third will get me to 35-45 MPH all revving the same as in first. My fiance thinks something may be wrong with the clutch plate but I would like to have a professional opinion before going into the mechanic. What is wrong how much is it to fix and can me and a couple of my fiancé's friends fix this without much trouble?