Cheap bluetooth remote controllers

I have seen bluetooth dongles for as cheap as $US 3. I am sure that I can buy them in bulk for as little as $1.50 3.7v and 5v relays are also cheap. Can a bluetooth dongle be simply connected to a relay? I have a couple of hobbies - hydroponics and raising fish -that would benefit greatly from being able to control lights, water pumps and drains remotely and with a timer. I would not need to send a stream of data via bt but rather a signal that would contain the id for the bt device as well as a simple "on" and "off" command.

No, you can't just connect a USB/Bluetooth dongle to a relay. If it were that easy they wouldn't be charging $140 for one.

The USB/Bluetooth dongle need driver from the PC to work, so it can't connect to relay directly. You can use this JY-MCU HC-06 Bluetooth Wireless Serial Port Module with Attiny MCU to control a relay for less then $20