On the other hand, from my talking to many people from every state in the lower 48 plus AK (including Puerto Rico) over the last 15 years or so, I can't recall any that don't require Coliform, nitrate etc. tests when a house is purchased and then with any problems having been corrected prior to closing on the property.
And in today's economy, a $100-200 is a bit much for many people but you downplay spending others' money because you seem to have a lot of it, plus you're from California.
The discrepancy between Culligan and Kinetico is most likely due to Kinetico wanting to oversell but, if there is no slime in the toilet tank, there is no IRB problem except possibly in someone's imagination or fear based thinking. But, although it's not necessary, shocking the well would be a good idea simply due to it sitting unused for 2 years.