Try the old fashion shovel. A soil auger will be expensive and very difficult to penetrate clay especially if it is dry.

Does he have clay or caliche? Caliche gets very hard and won't let water penetrate. I bought the awesome auger, works with a drill and I use it to dig holes when planting even when I'm at a spot the ground is not hard. It might be just what you're looking for.

https://www.awesomeaugers.com

Gemfire

I've an auger bit that - I know it was cheap because I am - that fits into a battery powered electric drill. It is about two inches in diameter and will drill to about 14-16 inches deep.

I've no idea what the thing was originally designed for, not the garden I'm sure as it was purchased at a hardware store in small town Nevada where nothing much grows because the town is on an ancient lake bed and everything is alkali.

I used it to drill holes through the calichi so the raised beds would drain if over watered.

Post hole digger