that's almost exactly the same dimensions as my grow cab. I use a 400w air-cooled HPS and grow about 24-28 clones in 2 litre bottles. If you were going for plants from seed than I guess you could get about 4-6 largish girls in there if you vegged for a couple of months.

I set my cab up for around 100 quid (made my own air-cooled hood with fixings from fan):-

ballast £35
HPS bulb £15
Carbon filter £30
Fan (centrifugal bathroom extractor from screw-fix ) £26