damn, youll be spending that much? Hell if thats the case then you can get all kinds of usefull shit to make life lots easier on you.
intake outtake fans for venting, light mover, dwc setups being your key things you need to get.
If your light has a plate glass cover that isnt to protect you if the bulb explodes, Its to keep it as airtight as possible so no heat escapes downwards to the plants. The only time Ive ever heard of a bulb exploding is if it gets wet while it on, or has oil residue from handprints on the bulb.
Now this brings us to another discussion since you said you have that much of a budget.... Venting that closet.
The better your air circulation the better your plants will look. If they dont get fresh air then they dont do well. What you really want is a negative air pressure inside of your closet...Which means you want more air going out than there is coming in. There is a couple options you have here to do that.
A) You can use an inline fan on your reflector so that heat isnt an issue in the room, and make a setup like you already kinda have with those pc fans but using 2 more inline fans and some vent hose to get a decent air exchange in the room. That should be just enough to get by with But I dont believe that it would cause a negative air pressure in there.
it would cost
B) or you could take into mind that your space is 5'long x 5'wide x 8'tall which is exactly 200 square feet of space in there.
There is another fan offered byu the same company for $80 and it can exchange 200 sqare feets worth of space in 2 minutes. That will deffanitly give you negative air pressure in the closet. I think you should also be able to vent the closet and your light with that one fan.
http://htgsupply.com/viewproduct.asp?productID=52479