Toon-Shading Terrain

I am doing a cartoon-style RPG, all the characters & monsters are toon shading. But not consist with terrain because there is no way to change shader of in-built terrain. What is the best way to achieve toon-shading terrain?

I can think of 3 ways that maybe can do it, but none of it is the ultimate idea solution to solve this problem:

  1. Use edge detection (post image processing), but requires Unity Pro.

  2. Create toon-styled textures to paint on terrain.

  3. Use terrain model instead of in-built terrain, not efficient and lose the advantage of in-built terrain.

This question has been asked a few times, but still there is no idea solution to this.

Let's sort it out here?

I assume you could create a new "built in" terrain. You would just need to script it to function similar or the same.