What's the point of undercutting by 500 gil?
The point of undercutting is not only to be the lowest on the market, but to convince people that they're better off teleporting to the town your item is listed in to buy the item. Teleports cost more than 500gil a lot of the times.. Lol...

5-10k is a nicer amount. Hell, on big ticket items you can drop it by much more than that and not make a dint in it.