I was surprised to see the drop as well. I had the same thought process as you with the Golems being released. I know the overall Beta Market has been dropping. I loosely been keeping track using my Beta collection value as the starting point.

I don't have the numbers in front of me but looking at my collections value I would estimate that my Beta cards lost about $500 of value out of a $6000* collection.

We are also starting to see some 3 cent untamed commons and I suspect the majority of the UNTAMED commons will follow that trend and at some point be closer to 1 cent. Again that's a short term guess / Long term I have no clue what the value of these cards might be.