Backstory: I recently ordered business cards from a large print website and had a horrible experience: poor user interface, incorrect order status online and late shipment. This is why Moo dominated the market. But I don't always want to pay the high quality and order a bulk option of cards, sometimes I just want a few (less than one hundred).
The Idea: A website that prints business cards targeted at small runs.
Deep Dive: Similar to moo and vista print, you would build a platform for users to upload images or pick from a few templates to create business cards. You would only offer two sizes, thick/thin and two finishes matte or glossy. This would be a no-frills, small order solution.
Validation: Moo took a big chunk out of crowded space with their premium cards. You could do this at the bottom with scale and little options.
Monetization: Straight forward physical product sales. You have to monitor your margins.