I want an electric drive train with the engine that works like a generator at a fixed speed. Don't think anyone offers something like this.
They exist, but I don't think there's currently any new models for sale in the US. I think they're generally called "series hybrid," or sometimes it's marketed as an electric vehicle with range extender.
I believe the Chevy Volt worked this way - you can see used ones for sale for around $15k.
That's the BMW i3 with range extender. It works pretty good for long trips. Probably 95% of my miles are electric though.
I think Dodge is planning a serial hybrid truck called RAM charger.