Price go up if your change price of item?
I wasn't aware of that. I believe that as soon as you place item in AH it tells you cost of posting it, it does not depend on price of an item. I might be wrong...
Item listing cost does not depend on selling cost. It is only a factor of what the item costs to vendor. Some items are cheap to vendor (like runes) so cost little to put on AH. Some have no cost at all or maybe one gold, like monster cards or recipes, so they cost almost nothing to list. On the other hand, rare gathering mats cost a lot to vendor, so putting them on AH will incur large listing fee.
Once you sell, sure, the AH takes %6, so it is dependent on what you sell for. But listing cost does not.
As for the rest of the OP message, that is how auctions works.