And like cars, replacement ebike batteries are absurdly expensive. $500-600 for a few 18650 and a BMS.

Part of it is that a battery pack is legitimately dangerous at that scale (so lots of testing/safety certifications etc). But those are one-time design costs that should be amortized.

I would really like to see some standardization around battery packs for both cars and bikes, so that it could become a commodity market for packs.