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A Mexican Red Knee for $100 seems a bit expensive to me. I would show you mine, but he's buried himself and is currently molting. I paid around $60 in your currency for one. Do you have anyone that give you a second opinion, to me it's expensive for the size, mine is 5-6 cm.
I have quite a few molting at the moment, but that could be due to me putting them all in larger enclosures.