Some non-standard auto carriers only require 500k However, most will not accept less than a million and that number has been pretty constant over the years.
Not sure I think you could go as low as 100k. But, probably would not satisfy any carriers. E&O is kind of a uncharted water for me. I don't sell it. Because most agents that are P&C licensed will purchase it for themselves and captives are offered group type E&O. I have never had another P&C agent by E&O from me.
So, I look into it once a year for my agency at 2mil and then leave it alone until the following renewal.