One of the material I would urge you not to purchase would be the Montessori Sand Tray.
There could never be a simpler DIY — find a small, deep tray or unneeded (shallow) plastic container and place a half inch of sand evenly in it. For a twist, you could purchase coloured sand (in red and blue, preferably) and use it for vowel-specific practices, or if you need your “sand” to be edible (with younger children around), you could use cornmeal for its similar texture. Beyond this, I would not deviate too much from basic sand — you want a material that will texturally correspond to the Sandpaper Letters and not distract from the work.
To teach your child how to use the Sand Tray, first select some Sandpaper Letters that the child is familiar with; show one card at a time, tracing it with your own fingers and sounding it out as you trace. Then place the card above the tray and trace the letter in the sand, sounding out the letter as you go. Shake the tray lightly to reset the sand and “erase” the letter. Pass the card and tray to the child and encourage them to repeat the actions.
Done! You can even do this activity on the DIY light box (as we did) for some extra sensory feedback.
We are working on S-A-T-I-N-P at the moment, as part of our Jolly Phonics curriculum.