Ok but you can also just either Welder to it or use R&B to set it up without having to worry about multiple evo lines if you wanted to use Silvally as an attacker
You'd still need all the energy needed to get the bonus effect. The Sunflora lets you ignore the cost of the attack, it doesn't make it zero.
Example: Reshiram & Charizard can use Double Blaze GX for 200 damage without energy, but to get the bonus 100 damage and ignore other effects, you'd need...
Knowing Pokemon, they'll probably throw in a couple of Steam Siege that was left over from when they overproduced. Although they have been good about it with the recent ReshiZard box, which only had one Roaring Skies pack.