1) You are missing Event, the parentheses/argument after onspellcast, and Endevent. If you look at the wiki entry for onspellcast, you'll see:
Syntax:
Event OnSpellCast(Form akSpell)
You should copy that exactly to your script, then add "Endevent" below it, and write your code between them. Also, in case you didn't know, the part at the end means that event is given the variable "akSpell" automatically, which is the base form of the spell that was cast, which you can refer to inside of that event.
2) But you can't use the OnSpellCast event in a script that extends activemagiceffect, because OnSpellCast is an ObjectReference event (See first line, your script extends activemagiceffect. Also, you have to use this kind of script for magic effects, so you will have to change the event, not what the script extends)
3) You should use "OnEffectStart" event instead:
http://www.creationkit.com/OnEffectStart_-_ActiveMagicEffect
With this, you do not even have to define the player, you can just do what you want on akTarget.
4) But wait, you want to change the magicka cost depending on the player's race. You can't do that because any event you can use is going to be triggered once you've already casted the spell and used the magicka. So what you should do is make the spell cost 0, and then in the OnEffectStart event, use http://www.creationkit.com/GetRace_-_Actor to check if the target is a vampire. It should be so m ething like:
if akTarget.GetRace() != VampireRace akTarget.damageAV("Health", 5) endif akTarget.damageAV("Health", 10)
Which also means you will have to make a property for VampireRace:
Race property VampireRace auto
I don't know if it's actually called vampirerace, or if the player race is changed to vampire when the player becomes a vampire. You might have to check in a different way.
The full thing would be something like:
Scriptname equilibruimifvampireornot extends activemagiceffectRace property VampireRace autoEvent OnEffectStart(akTarget, akCaster) if akTarget.GetRace() != VampireRace akTarget.damageAV("Health", 5) endif akTarget.damageAV("Health", 10) akTarget.restoreAV("Magicka", 25)Endevent
Hopefully this helps though.
Edit: Oh sorry, I did it inversely originally, so that it was magicka into health. Fixed now.