1992 Subaru Liberty Major Slipping

Soon after I bought the car started a rather loud whine came from gear box end of motor, the on a 10km drive it started slipping when changing cear and rpms went to about 4 or 5000, for short periods roughtly 1 second or two, then nothing, about 2% drive when in drive, after cooling for about 5 mins it works again, after about 2km it starts slipping again, just as bad as before.
I have only delt with manuals and older cars all my life and I know it as a worn presure or clutch plate, I was just afetr some advise on the cause and estimated cost on this issue if you could please.