I've just competed making the sandpaper letters. It took me 3 days and around 2 hours each day. I spent a lot of time researching as to the type of font and font size. I settled on Century Gothic, bold. However, it's not as difficult as I thought it would be.
Cardboard / Mounting board (also used by frame shops)
UHU glue / Art Gum (rubber cement)
I printed the letters and cut the shapes out with a penknife and scissors. I then traced the letters onto the back of the sandpaper. The I cut the sandpaper letters and glued them onto a mounting board which I bought from Tesco for RM5.90. I used pink background for the consonants and blue for the vowels. I didn't ruin my scissors although I read that some people did. The end result was of comparable quality as that of sandpaper letters sold by Montessori suppliers in Malaysia.