What is cheap Samsung smartThings hub extender i can get for a Samsung smartThings hub STH-ETH-250?
Welcome! First, let’s make sure we’re all talking about the same thing. 
What exactly are you hoping to do? That model doesn’t itself have any “extenders.“
It’s the primary controller for both a zwave mesh network and a Zigbee mesh network.
Both of these protocols work by having Mains powered devices pass along messages from other devices of the same protocol, which allows you to cover a bigger space.
But Zigbee repeats only for Zigbee and Z wave repeats only for Z wave, so it may be helpful to think of them as two different projects when you look at getting good coverage for your home.
What country do you live in? The device selection does vary by region.
For Zigbee, the IKEA pocketsocket is an inexpensive device that works well as a Zigbee repeater for most people. It’s available in many different countries.
You May be able to get it from Amazon, but it will be less expensive if you buy it directly from IKEA.
US:
UK:
For zwave, The region really makes a difference, so we would need to know that first. But again, typically the least expensive option for a repeater is a simple smart plug.
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