It makes sense, though, that restore magicka isn't a spell. I mean, spend magicka to restore magicka? Doesn't make much sense. If I had to make a spell like that, I'd make it cost 0 magicka and instead apply a damage health or damage fatigue effect proportional to the magnitude of restored magicka.
But if you have it open for spellmaking, then:
if it costs 1 magicka or more to restore 1 magicka, the spell is useless
if it costs less than one magicka to restore 1 point, then the spell is too powerful, unless it's something like 0.9 points to restore 1 point. Which still doesn't make a lot of sense.
If you want to leave it open for enchanting, then I'd probably make the cost 1:1, and have the player acquire the effect through a custom spell like the one I described up top (that uses health or fatigue to power the spell rather than magicka). But that's just my opinion.
EDIT: sun damage will only affect the player. I think that's hardcoded, but I if I am wrong, someone please tell me - I've always wanted to make my enemies fry in the sun.