Does this actually target the Avatar?
Yes. If your opponent casts this and targets your Warded avatar, you will not draw any cards and the Ward will break. Normal targeting rules apply (e.g. a spellcaster in the void or subsurface couldn't target an avatar with this magic, since they aren't in the same region).
How does this interact with damage prevention effects?
Damage prevention effects on the avatar will still apply to the damage from Searing Truth.
What do X cost spells count as for this effect?
Market
$0.25
Low
$0.20
Median
$0.25