Are you paying for electricity? This includes having your parents or landlord make your life harder when a massive power bill comes in. There is also a rather large difference between states
https://www.eia.gov/electricity/state/ (compare Oklahoma and Hawaii). Similarly location may also be an issue for heat -- if your new 500W heater means you need to stick your 1000W air conditioner on to balance it then that adds up a bit, however if you live in the Frozen north or up a mountain then . You did not mention noise so I guess that is not an issue, and if you are going to try to do this in a small room heat will be an issue.
http://www.tomshardware.com/reviews/nvidia-geforce-gtx-1070-ti-8gb,5311-16.html reckons some 180 watts under their torture test. Wrap the rest of a machine around it and that will add up very quickly.
What sort of timeframe do you want to make the price of the hardware back on? Are you going to try to sell the hardware at the end? Solo mining is not an option for many these days (and that is not likely to do much for you) so pool it is and these can be quite variable.
Trying to model future conversion rates for more conventional currencies is hard, something as incredibly volatile as crypto currencies is even harder. This also assumes the one you are on sticks around -- while bitcoin is still the big one (all the others being called altcoins) it had some serious uncertainties in the past year or so and the rise of ethereum was not because of any great political change or crypto failure of bitcoin but theoretically because it did something others had not really done before, as well as a bit of a gap between difficulty and price meaning it could be done on on more conventional hardware for a while. Even more annoying is predicting the future difficulty (your hardware will remain effectively constant but the number of hashes needed for a round may rise or indeed rise quite a lot) and at the same time someone could turn around and put out a FPGA setup tomorrow (they are field programmable gate arrays after all) or an ASIC could appear whenever for that given coin too and render your GPU pointless.
You can probably still get something done but you are asking all the wrong questions, or indeed the questions of someone not so versed in the necessary matters.
http://www.legitreviews.com/geforce...-small-tweaks-great-hashrate-low-power_195451 says 27 MH/s
You can then play with a calculator yourself if you want
https://www.cryptocompare.com/mining/calculator/btc?HashingPower=27&HashingUnit=MH/s&PowerConsumption=0&CostPerkWh=0.12
With normal numbers for the power bill and assuming same rates for some currencies you might get $30 a month, or more likely 20 if you are only doing it 2/3 of the time. That is years to pay off your hardware if the difficulty remains the same, which it most certainly won't (the review I linked for the hash rate already mentioned it going up significantly in the months around it).
