The mana cost is not noticeable once you level up a bit, so I don't mind that... Although come to think of it, since it's not a spell that scales in any way, and since at higher levels it becomes effectively free, that does create an odd imbalance between the gameplay at low levels, when 7 mana actually matters, and that of higher levels. So now I wish I could go back and change my vote. If it's intended to be a drain on your mana then it should probably scale its mana cost up automatically as you level (although I would rather it not do that, thank you very much!), but if it's intended to be a spell that's so cheap that it's effectively free, just cut out the middle man and make it free.
A couple other things on the subject of Ride the Lightning, though. One, I'd like to see its cooldown decoupled from the other spell cooldowns. It's a maneuverability skill, and it doesn't make sense to have it on your offensive ability cooldown. When you're running and gunning at bosses, this becomes quite noticeable. (Why didn't I dodge that bat! I was jumping! Oh wait, I was holding down my fireball too, drat.) Secondly, and I don't know how much coding trouble this would be, but I'd like to see its self cooldown decreased or flat out removed, and the flying problem fixed by simply not resetting it until you touch ground again. That would match a lot better with the standard conventions of platform games. And while I love to see Arcen innovating, in this case I'm feeling like the tried and true standard is probably the way to go.
Oh, and a final thought for some time down the road, this is a great skill for which to add in cosmetic variations. Green lighting, pink lightning, replace the lightning effect with fire or waves, etc. etc. Just a nice way to allow players to customize their experience. (Oh and when is the in-game hat store coming?)