Honestly, regardless of electricity, If I had the funds for an S7 (excluding shipping), I would go out and purchase one since it's on the cheap at the moment, and you get to get back what you spend just in right time before the halving. An S7 gives you $186 on monthly basis (assuming with current difficulty only) and not $300 as you were asking. It's price is $575 on bitmain (one fan) at the moment and if you were lucky enough to get your hands on one of the discount coupons , you can get it for $100 less so the ROI is even sooner with less $100 on it's price tag.
Smart money says, if you had the funds for an S7, you'd be better off buying btc instead of a miner to mine for btc wasting your electricity. The cost of an S7 includes not just the miner itself but also it requires a Power Supply Unit at least 1600 Watt, the electricity to run it and internet.
As others pointed, you won't make $300 in a month with only one S7. You're too late to the party. The diff factor is rising fast, thanks to all the idiots like you who bought S7 miners thinking these were money printers. Better to buy bitcoin directly than to buy miners to make bitcoins, the latter makes no sense.