please, if your not going to be productive or help the OP, dont comment with pointless comments. you could have easily told him that a HP wasnt likely politely and not have been so rude.
nate id say around an oz per plant if you train it well, id start topping it and lsting to get a nice sized plant with more nodes. i saw somewhere on here where you can top it and get 4 main colas but it has to be done at a young age. if your search around on here im sure youll find it. try google to. but a half pound is really really unlikely. now you could set up a perpetual grow and maybe harvest an oz or two a week, this could get you a quarter pound every month or so. look around on here, id try and go 12/12 from seed. maybe buy regular seeds get a male and female, pollinate a lower branch or two. itll give you dozens of seeds and you can start a 12/12 from seed and have good bud every other well ready to harvest.
only problem i see if your cab is pretty small so i would probably treat it like a pc box grow, one plant, lsted and topped, maybe screen of green?
hoped this helped mate