If it only has to signify its presence, I would have thought the NRF24 could do that without an Arduino, I'm sure you could do it with bare bluetooth. But some of those bare-essentials ESP8266s have their own intelligence and and cost about the same anyway. The real cost is surely going to be in the packaging.
Another thing you need to be careful about is re-inventing the wheel. It's the sort of thing that would be a lot cheaper to buy than make.