Last time I compared prices, battery powered mowers were priced at a premium compared to gas powered units and the availability and pricing of replacement batteries was not something easily ascertained. Some of the mower blades seemed light duty compared to regular mowers, too.
The Cub Cadet zero turn units with steering wheels seemed to be priced about $1,000 more than their regular ZTRs, but have higher slope ratings. If I were going to pay a premium for a hillside mower, that's probably where I'd consider spending my money if the slopes I had to mow in a yard were within their slope ratings.