Insight: Boots used to be bugged and would not take material into account when enchanting. This meant they were extremely cheap to enchant and many people took advantage of it thinking it was always supposed to be that way, but it was fixed. I can tell you that my boots cost something like triple what people used to talk about them costing. Also, some new crafting gear costs more or less to enchant as part of its desirability.
As far as I know, crafting bonuses can't stack because of the way NWN works. So certain combos are only chosen for their secondaries.
