Automatically no 3d printed case is worth $300 because it's not possible to make it good enough quality.

A metal and wood case could be worth $300.

A good design is worth something, and a good printing job is worth something, and the convenience of a service is worth something, but no amount of good design and quality printing job and service convenience can make a 3d printed case worth more than about $50 before shipping, and it would need to be somehow pretty special design to overcome some basic material and process weaknesses and still be functional and look good to be worth that much.