1997 Cavalier manual, stuck in 3rd???

I was driving today and while shifting I heard a "POP", I go to down shift and nothing. My shifter isn't doing anything, I think I'm stuck in 3rd? The question is what is wrong? Snapped linkage cable? Shifter? What am I looking at fixing and does anyone know an estimate price on fixing this? Is it something I could do?
Any help would be appreciated.

Check the shifter cables at the transmission. From what i have heard i think something in them was made of plastic and they like to snap. I haven't toyed with the manuals on these cars too much so its hard to say.