if difficulty never increases and price never changes - about 0.0002148 BTC or $2.25 a month. but those two things always change so it can go up or it can go down.

these are not about making a fortune, its a hobby miner - to make it easy for anyone to mine and contribute to the network. now if you solo mine with it, the cost is very little as its basically like a 100 watt light bulb in usage.

but if you play that lottery and mine solo and win... let's just say you will be very happy