I recently got 7.4kWh at $160/kWh grade B cells for what it’s worth. Surely there are better deals out there, especially for used cells.

Even 4x as much is still way closer than what I've thought. This is not commercialised on a mass scale yet, but batteries are and have been for ages. Billions and billions of dollars got invested into cheaper, better and faster. Even 4x just seems right around the corner if you consider just how much work went into making batteries cheaper.