I assume that when anything goes wrong with a BMW, and I assume it will relatively quickly, the repair costs will quickly close the gap on any initial savings.
There's a lot less to go wrong in an all-electric vehicle. Not saying you can't have issues with fans or the seat-heaters (ahem), but you're not looking at an engine rebuild or even oil changes down the line
The original Fiat 500es were a train wreck, even for a Fiat. They were super cheap, but all the stories of the owners who carried around specific wrenches in the back to disconnect and reconnect the battery as the easiest fix finally convinced me to pass.