To answer your question, as a rule of thumb I would say that:

Canvas kilts in the sub $100 range are the social equal to blue jeans.

Traditional wool heavyweight kilts between $200 and $500 (not even counting accessories) are black tie.

What these guys are saying is that there are a lot of kilts in the $100 to $200 range that could be either (with the right accessories) most of these are "Poly Viscose" or 4 yard medium weight wool.

Now my problem is that I bought a all black polyester kilt specificly to wear as a casual kilt but it is a little too nice for that while being not quite nice enough for formal wear. It will become club wear only I think.