Rememebr,
A HARP character has multiple spells (from 1 - 20 max per profession - generally!) that he can start learning early and can escalate as he gets betetr - learns more ranks.
DnD charaters have weak spells that cant be scaled or changed - you can only learn a different spell that has a similar effect (ie. Acid hand is touch and does 1hp, then Magic Missile does more damage but limited to a max effect), increasing to more powerful spells at much later levels...
These are different tyypes of magic systems and this is how it is supposed to be. Changing the PP cost isnt the answer.
Dont make it into a Rules issue it is a personal GM issue. if you dont want people of low levels have the spell then just tell your players that you are making a house rue: "No Long Door until Level X".
Problem solved.