AC Blows Warm Air

today i replaced the blower resistor in my 96 Cavalier and i think the freon needs to be recharged, because the AC only puts out warm air, it used to only work on the highest setting

does anyone know how much it would cost to have a mechanic recharge the freon, or can i do it myself??

I have a 96 cavalier and my compressor is out. i had freon put in before i knew the compressor was out and it was about 25 dollars. you can now buy coolant for your ac but i would get the freon.