This isn't a new idea, but it's a fun one I haven't worked out the details of myself.
Healing Costs the Healed. Healing spells - specifically Minor Healing, Major Healing, and Great Healing work as written. As is normally the case with beneficial spells, the target must be willing (or unconscious, which here is assumed to be tacit willingness.) However, the caster pays no energy cost. Instead, the target of the healing spell pays any FP cost and is healed any HP. The caster chooses the level of healing, but if such healing takes the target below -FP the spell fails automatically. Reduced cost for high skill is applied before any cost to the target.
On a failed casting, the caster still pays 1 FP if the spell would have cost anything to the target.
For example, Reverend Al Murik casts Major Healing on his wounded buddy Vryce. Vryce has 15 FP, 30 HP, and has suffered 23 HP of injury and has lost 4 FP due to combat and movement; he's currently at 11 FP and 7 HP. Al wants to heal him fully and specifies the casting at 4 energy. He has skill 16 and thus the spell is -1 cost, for a final cost of 3 FP to Vryce. The spell heals 8 HP x 3 = 24 HP of injury, bringing Vryce to his full 30 HP and dropping his current FP by 3. He's fully healed, but much more tired - he's at 8 FP and 30 HP. Al's FP are unchanged.
Alternative: Both Pay. Alternatively, the caster always pays 1 FP for any spell that would otherwise cost points (in other words, if the net cost to the caster would be 1+, after energy cost reductions). This is in addition to the cost to the beneficiary of the healing spell.
You could probably do this with a lot of buff spells - Great Haste already does this to an extent, since it charges both the caster and the subject 5 FP. If all buffs cost the caster and the subject, you'd see a much more cautious approach to buffing.