Can I walk from the US into MX to rent a car at the airport and vacation around Ensenada (no flight/no boarding pass)?

You have to go through Mexican Customs

Hi Doug, you need a boarding pass to cross through CBX.

No you cannot, i flight ticket is required

I don't believe this is a product CBX sells.

As far as I know you need a boarding pass.

No. Plane ticket is required.