Mk V Furnace

Using shipment prices is a good way to determine when cantina energy is worth it as well.

150 crystals for 3 shards.
100 crystals for 120 energy. At a 12 energy battle, that's 10 battles. At a 1/3 drop rate that's 3.3334 shards per cantina refresh. That means you are paying 100 crystals for 3 shards for the first two cantina refreshes, after that it is 200 crystals for 3 shards, 400, etc. That means it is actually cheaper to farm characters out of shipments than cantina after your first two cantina refreshes too.