Good luck with it all. I was mining with a BFL 50/60 Ghs for a wee while. I think if you use
http://www.bitcoinx.com/profit/ you will tell with you should be getting and an idea of outlay etc.. Thee has been large difficulty increases recently driving costs of these machines down so it's a calculation game.
On the plus side, mining is great, miners are totally required so you are doing a good thing. All the calculators base forward thinking of profit on current prices, you really need to look forward I think, so what seems bad now may be better later. Be careful off large swings in difficulty though as it can kick into your resell costs.
I would not like to ponder a guess at the price in a month, but if you take difficulty increases into account you can see your rig mining at 30-50% in that time. It's not entirely linked to cost but a good indication.
In any case, best of luck and happy mining!!
