This is gonna sound kinda lame, and it's probably not gonna help as much as you want...but always planning on using 1 mil SP is a good idea.
Even though some skills may not seem important now, you may end up wanting them when you reach level 90. If you are building an axe-warrior you will want to attack with those skills while using cleric to buff yourself and party members (no duh). That means as you're reading through and picking cleric skills it might seem easier just forget about adding the offensive ones and whatnot. This will get you to 90 in good shape, but later on you may wish you had farmed yourself more. There are always those weird skills that look useless but aren't.
Anyway cleric is an SP suck so I would just be safe and set yourself up for needing a mil. What really helps is powerfarming at ongs and dying over and over to gain close to a mil (start at level 19 then level up to 29, and die back to 18 or 19 again) that way you can keep a 0 level gap ALLLLLL the way to 90
