As of now, you may want to check out the s9 after halving. The risk is way too high rn imo, so if your electricity rates stay like that, you might want to get one. Prices might rise, but better to know you won't lose it all than to gamble on the price of BTC going up to the point where you'll make money.

Since you already have S7s, the operating cost will ensure you a slim profit over a short time, then nothing. The halving won't bump you too much, but after that, consider a newer miner. Halving will force most , if not all people with even low electricity costs to get a newer generation one just because of difficulty.