How about using Infuse Nature to grant fast healing as it is a very similar effect just front loaded.
If that standard duration of a spell is 1 minute (10 rounds) then if you divided out the bonus from Infuse Nature across 10 rounds you'd get something like...
Fast Healing 1 = 2 MP
FH 2 = 4 MP
FH 3 = 6 MP
FH 4 = 7 MP
etc.
The MP cost would get less as you increase on the chart, but I'd recommend that it be kept at 2 MP per point of Fast Healing to prevent too much abuse from extended durations.
The bonus is similar to the healing you'd get with a Heal as well (on average). The only problem that I see is when the duration is extended. Then for 5 MP you'd get Fast Healing 1 for 10 minutes which would heal 100 hp, and you'd have to pay 12 MP to duplicate this with Infuse Nature. Although enduring curing for 10 minutes (13 MP) would grant 3x this much, which is closer to what FH 3 for 10 minutes (9 MP) would cost.
If that standard duration of a spell is 1 minute (10 rounds) then if you divided out the bonus from Infuse Nature across 10 rounds you'd get something like...
Fast Healing 1 = 2 MP
FH 2 = 4 MP
FH 3 = 6 MP
FH 4 = 7 MP
etc.
The MP cost would get less as you increase on the chart, but I'd recommend that it be kept at 2 MP per point of Fast Healing to prevent too much abuse from extended durations.
The bonus is similar to the healing you'd get with a Heal as well (on average). The only problem that I see is when the duration is extended. Then for 5 MP you'd get Fast Healing 1 for 10 minutes which would heal 100 hp, and you'd have to pay 12 MP to duplicate this with Infuse Nature. Although enduring curing for 10 minutes (13 MP) would grant 3x this much, which is closer to what FH 3 for 10 minutes (9 MP) would cost.
