Cheapest SmartThings compatible relay?

I’m looking for the cheapest relay that can be connected to ST. Voltage doesn’t matter, as I have lots of spare transformers, relays, etc.
Just need to be able to send a simple on and off signal, some simple circuitry will handle the rest.
These would be used for various applications, like powering on PCs, fireplaces, gate, solenoids, etc
Also is it possible to have a device hardwired to the ST hub?

Sonoff would be what you want. There are many threads on them here. Made in China Wifi connection.

Just ordered one. Couldn’t have asked for anything better!
Thanks, can’t wait to try it out.

Are there any wifi independant relays similar to sonoff? I do not trust my wifi router and I wish to depend only on z-wave or zigbee connection to hub… I torn down Ikea Tradfri smart bulb but there is 95V ouput and I can not use that voltage for any relay.