The very first thing i advise you to do is to test the acoustic responses in the room.
Take out everything except your computer (if you are going down that route) and monitors/microphone. Then you will need to obtain the REW software (Its free if you join the home theatre shack forum). This will allow you to take some readings of the frequency response and reverb times in the room. With this information you will know which frequencies to treat.
As for the treatment itself, i (with the help of my wife and mother in law) built all of the bass traps and absorbers myself and treated the whole room for less than 500 euros.
You should aim to have some treatment on the ceiling and a reflective floor (no carpet). This will give you the hard surface/soft surface approach which is common nowadays. The reasons for treating the ceiling instead of the floor is that carpet is unpredictable acoustically and floor reflections sound more natural. Also our ears can understand reflections from the floor much easier as the distance between our ears and the ground doesn't change a lot and the distance between our ears and the ceiling (or sky) changes drastically all of the time.
What i did was to hang some "Clouds" on the ceiling (Absorbers built the same as for the walls).
If you need expert help (and i did) then join the John L Sayers forum, dedicated to studio acoustics (sorry to promote other forums here, but they were a big help in this) and they will be more than happy to help.
Good Luck,
TCT.