This is my own 3D model that I built from scratch of a TARDIS and slightly modified it to become a ring box - all you need to supply is a foam insert (optional) and ring! It's a sleeved style box with a good fit, so if it's grabbed from the top the bottom won't just slide out - it needs to be pulled out.
Great idea for an extra geeky way to propose to the special whovian in your life!
ring and foam box not included
The box bottom has to be purchased separately as I haven't figured out how to bundle them together on here.