Ok, so what is the cheapest way to get extra key that will start the car? Only have the 1 key now. My kid just got his license and I need an extra key just to be safe.

https://www.thebmwminipartstore.com/

is a real BMW dealer. So you can order a non-remote Genuine BMW key from them that will include the EWS chip. No remote functions, but will mechanically unlock the doors, and start the engine.

I got 3x "valet keys" from them back in 2014 to serve that purpose (3x kids). The valet key cannot unlock the glove box, and has no keyless entry functionality, but can do everything else.

I don't know why they make things so confusing, but they do (BMW, that dealer, etc.). Key types, names, ultra-low resolution drawings, part numbers, etc. seem to be constantly changing, as if they do it on purpose as a security procedure. When I got my valet keys, the guy on the phone telling me what they were did not really understand what they were, only that they did not have remote functionality.

From my notes, here are names, part numbers, and old prices on a few different keys. All of that was perfectly accurate at one point in time, and I would not be surprise if it is all wrong now. But it might help, so here's a copy and paste:

51 21 8 213 932 $39.59 Service key. Plastic wallet key
51 21 8 213 931 $39.59 Spare key. Valet key. superseded to 51 21 7 124 770
51 21 8 236 594 $39.23 EWS III key (per the bmw mini parts store.com - shows …931 superseded to this)
66 12 6 955 750 $154.65 Diamond key. Master Key with remote control.

Possibly of interest, but I made one of those ebay flip keys for two different cars.

It was a pretty straightforward process other than finding someone to cut the key for a reasonable price, which is difficult. I even bought the Chinesium key cutter machine from Alibaba or whatever. I was never able to make that work. I got several keys that would open the door just fine but wouldn't turn the ignition.

I second wpolls assertion that the chip itself requires no power. i know this because the chip comes in a little plastic bag separate from the key itself. after you program the chip to the EWS, you just stick it in the case of the flip key with adhesive.

I have never tried it, but it'd be easy enough to remove the chip and see if it will work outside the case, and test distance/proximity as well as how quickly the chip is read once the key is inserted and if there needs to be a 'sequential' event: chip is read, key inserted, or vice versa.

Interesting side note: These off-brand chips DO behave a touch differently. When I press the hatch-lid release, there's a 5 second delay before it opens. The door locks also have a slight delay, although not nearly that long. But it's certainly not a deal breaker for a cool flip key ; ) Also, the advanced functions such as rolling down all the windows...none of those work.

I like the idea of the $20 key-fob only though.