Well, this is what you originall posted...

"I have a 2003 Cavalier.  The climate control knob that switches the vents
your heat and air come from has broke somehow.  I cannot get the knob to
turn and stay in position.  Has anyone had this happen before?  If so, how
do you go about fixing it and what about the cost?  Thanks guys for your
help!!"

... so it sounded like you had a broken knob.  I haven't heard of this
happening before but I'm sure it must have - at least once.  Do you know
anyone that is mechanically inclined?  You could get a new control head from
the junk yard and throw it in.  I've never done it on that car, but it
really shouldn't be that bad a job.  It's one of those things you just start
working your way through.  If you don't have a friend who does this stuff
then almost any garage could do it if you get the parts from the junk yard,
or they can get new parts through the dealer.   No idea on cost.  You should
be able to call the dealer and get a quote.  Any local garage would be
cheaper.