As far as I know, luck bonuses don't stack. If you can find a counterexample, please post it. The closest thing I can find is that you can stick multiple luck bonuses on one item without the usual +100% inflation in cost. So, a ring that gives +2 luck AC may cost 10k, but +2 to AC, saves, and skill checks is 30k instead of 50k. Maybe that's what you were thinking of.
These other guys have covered the other types.
The reason the Luck bonuses, etc. cost more AFAIK is because they're types that most characters will never have, so it's effectively an untyped bonus (which I'd charge 3000*n^2 for, if I allowed them at all, which I don't, because otherwise you'd just take a dozen slotless +1 items for the price of a +5). I mean really, what are the chances you'd find two different items providing a luck bonus to the same ability? A lot less than finding two items with Deflection bonuses, I'd say.
Insight bonuses are hard to find. Combat Precognition (AC), Combat Prescience (attack rolls), Armor of Insight (AC again), and one other for dodging traps... that's all the insight bonuses I can think of offhand, and they're all psionic powers. It's a very rare bonus, like Sacred or Luck, so it costs more. You're almost never going to have a conflict with another item.
Compare to Natural Armor. Besides the amulets, there are spells like Barkskin that give it. And Polymorph Self/Shapechange. And monster races in general, or spells like Bite of the Werebear (on the WotC website), or whatever. It's not uncommon to see a character with a Natural Armor bonus, so that's why it's a bit cheaper.
Dodge bonuses are more common, and stack with themselves (which'd make them as good as untyped bonus) but they're lost when denied your DEX bonus, so that drops the cost down a category.
Anyway, that's the logic I used, your mileage may vary.
Makes me wonder why a luck bonus is so damn expensive now.
