Pure Vermiculite is the easiest to grow in. In a coffee mug, I use three parts vermiculite, mix a few seeds (oat grass) in the top. I just stir dry with my finger. Then I add two parts water. I don’t have to touch it ever again.
I do one ever two weeks as the roots get to crazy and thick and the grass dies.
The initial cost will be high ($20-$30 for 50 cat grass or more), but over time it is cheaper than buying grass kits ($5 per kit).