clutch not working smoothly

I have a problem with my clutch which is a big issue because I normally love driving my mustang but not lately. It grinds often when I go to put it in third gear and sometimes in 4th. The clutch pedal is all the way down and there seems to be just as much pressure in the clutch pedal as would be normal. If I shift slower than a normal rate then it won't grind but will go in... still pretty rough. It feels like it takes a few seconds for something to stop spinning so that I can slip the gear in. I don't have the know how to fix it so I will be taking it in, just want an idea of how much it may cost and what exactly is going on. Thanks for any help.

Sounds like either the synchronizers in the tranny are getting worn or the clutch throw out bearing may not be extending all the way