A hundred grams of this realistic and easy-to-apply 2mm Basing Grass will cover about 2.5 sq ft so you can apply as little or as much as you need to without breaking your model train budget.
WWScenics Refill 1000ml 2mm Winter Static Grass - 100g Model Rail Scenics G2-031
WWScenics 2mm Dead Static Grass - 500ml Canister Model Rail Scenics G2-053
WWScenics WSG-4008 4mm Spring Static Grass 500ml Canister
WWScenics WSG-4021 500ml 4mm Autumn 50g
WWScenics WSG-6012 500ml 6mm Summer 50g
WWScenics 4mm Summer Static Grass - 500ml Canister Model Rail Scenics G4-017