On 120 mm there are many natural materials you can use without going to the expense of buying ready made items . Small stones , earth backed in an oven and worked through a sieve , twigs and small pieces of wood are just a few . I have a friend who when he sweeps his drive way sieves it out for dusty terrain effect . Building materials can vary so much from country to country but one thing I would recommend is Tile Grout , it comes in a wide range of colours you can get all the earth colours you'll need and it's cheaper than modelling type terrain products . Just make sure you cover the area's with white wood glue first for good adhesion . All the items I've mention can be painted or highlighted using all the different paints modelers regularly use . I use many and more of these , the only thing I ever buy is grasses
chippy