I use a clip-on macro lens for my iPad, plus a little axial light box that I built out of LEGO bricks. You can check out my coin photographs on my ebay link. For less than $10, I think it works really well. This lens looks similar to the one I bought:
https://www.amazon.com/KINGMAS-Univ...p/B00FTSG35E
https://www.amazon.com/KINGMAS-Univ...p/B00FTSG35E