Using the Estimating Magic Item Gold Piece Values table on page 285 of the DMG, how do you accurately price a portable hole on page 264 of the DMG. I am trying to find the accurate pricing formula for a standard portable hole so that I can then just increase the caster level of the item. Currently,
a portable hole has plane shift that is a Sor/Wiz Spell of 7th level or a cleric spell of 5th level and a caster level of 12.
I am assuming that they used the level of the creator cut it in half to get the 6-foot diameter of the portable hole; so if you made the hole when at 20th level it would then make the diameter of the hole 10 feet.
What I am trying to figure out truly is a price for the increased manifester level of the same item.