The cost is really the printer itself and the time invested. This would probably cost ~1$ of material, and take ...3 hours of printing?

The case doesn’t need any special material so whatever’s cheapest usually works, especially if all you’re worried about is protection and not style. In face you technically don’t even need the case, the one I develop the firmware on is bare, but still, you shouldn’t have to spend more than probably $10 USD, maybe cheaper if you can find a local maker space to help you print it.

I don't know the exact cost, but there are online services to do 3D printing for you, like Shapeways. I've used it before. It made more sense than buying my own printer. I downloaded a design from Thingiverse.com, uploaded to Shapeways.com and ordered the print. They will give you the price before you order.

Maybe a friend or maker space or local library would have the printer and not cost much at all. Idk how much an online print place would charge, apologies.

You can get a reliable plug and play printer for as little as $500-600, though it will take 15-20 hours, if you’re technically minded, to learn to get the files to print. The material will be around $30-40 at retail prices (it’s generally only sold by the kg).

You can likely send the files to a print house and get them printed for just $100-200.

(Someone will claim that the $99 Ender and a roll of $9.99 genetic PLA will work. They are technically correct in the same way that your grandmother can edit photos for free by setting up Arch Linux on a $100 PC from Goodwill.)