Here's a cheap idea that started me off a long time ago and I still use once in awhile when I'm to tapped for other resources:
Find an old desk, make place in your closet, flip it on it's side inside the closet, Paint the inside flat mat, latex for walls is excellent and cheap for this. Drill a hole for ventilation *FAN > inline fans are cool and quiet and will move enough air for a healthy set up. Go to hydro store, purchase a pre fabricated mogul socket, purchase a 6700k CFL to fit in the mogul socket, hang it on hooks chains inside the desk. and presto, you got yourself a grow cab.
I would use this only for vegging though, by flowering time you should have gotten paid from work or crime and should invest in another socket set / and another CFL (This time go with 2700k to 3000k CFL light bulb), hook the light to the clothes bar and you now have yourself a flowering chamber
make sure to add a cheap fan for ventialion for you flower chamber and your good to go.
Lat but not least, if you do not want people to know (stealth, and have a bit more cash to spend), invest in a carbon air scrubber. and run it in the closet with the closet door closed 99.9 % of the time. When you need to do maintenance make sure before you opne the closet to have a good air flow in the room to ventilate it before/during/after maintenance so that the heavy smell is not so "Heavy" ^^
Have fun, hope this helped, and if I had to estimate how much all of the above cost it would run you around mmmm 300$ Canadian. Oh yeah, I'l leave you with this comment which I heard actualy 3 days ago from the hydro store owner .... "You can never have to much light, it's the heat that accompanies that light you need concern yoursefl with!"
F.y.i. CFL's produce very little heat and I touch them daily, they don;t burn to the tocuh! so u can have you plants up to 2 inches away from the actual plant top
Take care