Well, with no consideration of multipliers, then make your own estimation for demon race for PP dev., and apply it. It is easy.
In RMSS/RMFRP it is not used the old system PP/lvl, PP dev. is linear to less PP while more level.
In any case, it is not recommended that, if you use the PP/lvl system because it can be more easy to apply (a simple multiplication to estimate the creature PPs based on its level), use more than 7-8 PP/lvl, as in other cases it can be an abuse.
That is for base PP, now it can has spell adders or PP multipliers, or other special considerations (see bellow), but that is another story.
i.e., you can give 'lords' the talents (maybe I don't remember well the names) 'aura' and 'archmage', the 1st gives you +1, 2, 3 or 4 PP per rank dev. and the 2nd makes your PP dev. skill everyman, so the ranks are doubled.
So, for a demon lord with lvl.75, assume that we use a base of 7 PP per lvl for demons, as they are like gods, apply the maximum talents, aura(+4) and archmage, we have a total of: ((7+4)x75)x2=1650 PPs.
See that we apply the major talents if the demon lord is a spell user, if it is more like a warrior type, but with magical powers (it is rare a high lvl demon that can't use spells), we should use others more appropiated, like only the aura(+2), because it surely developed another talents (to have those OBs or HPs). So our warrior-like demon lord could have: (7+2)x75=675 PPs.