The only cost she has that's "too high" is her heal, everything else is manageable. With that said, her heal actually heals nicely, since it's a low cooldown sustain as opposed to taric/soraka's burst heal which have near 20 second cooldowns AND high mana cost. On top of the sustain, she gets poke.
I'm not saying you're bad, I'm saying I don't agree completely. I have played her a few times, she's my favorite support, but I don't main support. However I found that a philo + chalice and my mana was just fine.