A lot of good things about using VCT:
The break pattern is very similar to concrete/rock crack patterns, or you can score and snap it in a straight line. Free samples are easy to obtain, but even if you have to buy some, it's available at any big-box home center and it's dirt cheap. 60-70 cents a square foot, and in theory on square foot will base 144 minis.
This is just a 2"x2" sample, similar to the one used to base all 6 models above:
For me, the tile is free, and it took only minutes to prepare all of these bases (of course, drilling and pinning the models to the bases took some time, but basing plastic models this way would take very little time).
It could actually be used to produce a very similar look to Les Bursley's bases, here. Someday, I'll get some paint on these and provide an example of a finished product.