Sometimes both vacuuform or donnacona board scenic brick are impractical. The set for the Munchkins in the Muppets Wizard of Oz, for example, has a vast background of miniature yellow bricks. This would be difficult to achieve with CNC sheets, as the grout lines are so fine, it would be difficult to maintain them when applying the scenic sandy slop. Without such a protective layer, the bricks would also get easily trashed by the unit (no offence).
Another solution is the 'doll house' brick method. This too is quite affordable; It requires good Scenics.
You can set up a cad file, similar to the one used for the donnakona CNC sheets, with your custom brick size, and have them cut out on paint mask by the local sign shop. You are then left with a 'web' of grout.
The Scenic Painters can apply this web to the raw flats, then apply a thin layer of spantex/sand/paint/glue mix. Once its slightly set, you can quite easily pull off the web, leaving the 'mini-bricks' in place on the flats.
Once they have dried, they are very workable and hold up tho the wear and tear of shooting.