Is the cost high enough to prevent abuse with multiple Sky Blitzes in one turn?
No, it's not. But you need, to play more then one sky blitz in one turn, more then one pentagram as well.
Further, even with 6 pentagrams in your deck, this will still be at least as unstable as a SNBow (Since there is no guarantee you will draw it.)
I guess, with 3 or less pentagrams, it's pretty useless to hope to be able to play more than one sky blitz.
So my assumption on a "good" Mono Airborne Entropy deck would be something like
7 Towers
6 Pendulums
4 Pentagrams
6 Amethyst Dragons
1 Sky Dragon
4 Sky Blitz
So, to play such a dack, you need a good amount of sky blitzes, a good amount of pentagrams, a good amount of flying creatures and a good amount of quanta. And fitting all that in one deck, you will want shards of freedom as well to get above shields and gain protection from CC. I don't think that a deck is too easy to built and I don't think that it would be faster or stronger than mono air in any way.
But OTKs will have new possibilities and combos, because they can, with one pentagram out, play at least a second skyblitz and probably achive the OTK with less cards and probably faster as well.