From August 2019, the latest price is $8,500, still well short of $30K:
https://www.autonews.com/sales/nissan-leaf-buyers-dealers-worry-about-replacing-worn-out-cells
[”A refurb program is needed to help owners who were affected by Gen 1 vehicles,” the Hattiesburg, Miss., resident told Automotive News. “I believe that these early battery failures are part of a learning curve that was passed on to the consumer. Nissan offered a battery replacement program for $5,500, but unfortunately they quietly raised the price to $8,500.”]
I think that’s more than the cost of a rebuilt/used engine and transmission for the typical Nissan econobox.