Considering this is a client sided edit, you are asking in the right place.
What you want to edit is skillinfolist.lua (lua files/skillinfoz/)
Simply add
SpAmount = { },
In the brackets, add the sp cost of each levels seperated by a comma and it should work.
This is an example for Teleport which is useful to have the toggle option for lv 1 without the menu pop up and level 2 for both options :
[sKID.AL_TELEPORT] = {
"AL_TELEPORT";
SkillName = "Teleportation",
MaxLv = 2,
SpAmount = { 10, 9 },
_NeedSkillList = {
{ SKID.AL_RUWACH,1 }
}
},