With the release of the iPad mini 4, Apple did not update its smart case. It sells a Smart Cover and a protective back. The major downside to this setup is what Apple charges for it. They charge $40 for the Smart Cover and $60 for the silicon back. This brings your case purchase up to $100! I'm usually a fan of premium quality cases, but $100 is way overpriced.

For my wife's iPad mini 4, I picked up a cheap knock off on Amazon from JETech. For $10, it basically serves the same function as Apple's previous smart case. It comes in a number of colors (black, purple, green, red, grey, etc). While it's not as nice as Apple's, it's $90 cheaper. I'd save the money and upgrade the storage on your iPad.

Get it on Amazon for $10-12, depending on the color.