Can you say where you can find a TS100 for ~$40? The cheapest I'm seeing is $50-55. Also, are there different versions you need to worry about or are they all

Can you say where you can find a TS100 for ~$40? The cheapest I'm seeing is $50-55. Also, are there different versions you need to worry about or are they all the same? I assume you only want a "MINI TS100" vs. some of the other knock off brands.