I guess you mean what is the special price on the armour table?
non-magic or magic armour up to +3 is of the first type. Armour that is +4 or +5 is of the second type. +6 armour is of the third type. The cost of the 'special materials' (and the greater AC) is included in the cost of the magic armour. So.....
An example using leather armour type:
A) Non-magical, +1, +2, +3 leather armour gives an AC bonus of +2, +3, +4, +5. The material used is leather.
B) +4 and +5 'leather' armour gives an AC bonus of +7 and +8. The material used is Feyleather (bleh!)
C) +6 leather armour gives an AC of +10. It is starleather.
Not very well spelled out in the PHB but confirmed officially by customer service at some point.
Makes Plate ACs interesting from non-magical to +6 the AC is: +8, +9, +10, +11, +15, +16, +20. The jumps are at 16th and 26th level.