I don't regret getting the large DMT in red and prefer it over all the stones out there, but they don't come cheap.

Many cheap stones are just that. Stone, natural or man made, come in many forms and even sharpening enthusiast argue of whats good or not.

Get some auto wet and dry sand paper and a mouse mat. Thats all you need to start.
https://www.youtube.com/watch?v=nnkl1BRRrSQ