First of all, his asking way above it's price ($637 in BTC on Bitmain website itself). Assuming that's 2nd hand so even worst, better buy directly from their website instead. You could earn around $190 per month, assuming the difficulty doesn't changes (which it does all the time so it could be a little different result).
Actually, with his 0.25$/kWh. He is not going to earn anything. He will have to pay more in electricity than he will earn
BTC with mining. 0.1$ is quite too high. 0.25$/kWh is ridiculous.
Yes, it will not be a profitable business. Your buying second-hand miner and if you face any repair than it will be even worst.
Since your electricity charges are so high, you will not make any profit with even new miner. Try to explore, whether you can use solar electricity.