There are indeed smaller, less powerful, and therefore more gas efficient, engines than those from BMW.

But overall BMWs are pretty good when it comes to gas usage per “engine size”.

around half a gallon, not worth it

Not worth it to you. But imagine a whole planet using it on a regular.

I bought a used Airport Express on eBay a couple years ago. Need it to stream my audio receiver to my speakers so I can play music from my phone over my stereo setup.

SUVs are pointless, so yes, please get something normal.