I wonder what format the Smash Bros. DLC will follow.
Mario Kart 8 DLC is 3 characters, 4 vehicles and 8 tracks (2 cups) for $7.99.
If they go down a similar route for Smash, I'm thinking 2 characters, 3 stages and 4 alt costumes per DLC pack, $7.99 a pop. That's a damn good value, especially if they do 2 packs for $11.99 like Kart did.
It's also a possibility that they might do 3 packs - 1 for characters, moves and costumes, which would be for both 3DS and Wii U; and 2 stage, music, items, AT and trophy packs, one for each. I'd imagine the character pack would be priced a little higher than the version-exclusive pack, but both might be a little more expensive than the MK8 pack, though it'd still be relatively cheap considering the attach rate they'd be aiming for.
For actual content, I'd optimistically put it at 3-4 unique characters and new clones, 1 new costume or palette swap for each character, 1 new custom move per character, 4 returning stages per platform, 3 new 3DS items + The Fan, 4 Wii U items, 2 new 3DS ATs + Isaac and Ray, 4 Wii U assist trophies, 6 new 3DS stages and 6 new Wii U stages through all three packs.