Here are a few homemade craters.  These are made from aluminum pot-pie pans.  You can buy these in bulk from the grocery store for a few bucks.  You will get more than you need.  Flip the pans over and squash the middle down.  Carefully shape them as desired as you smash them.  I then cut the edges into irregular shapes.  Glues on some rocks and apply some texture, then paint. 
 

 A comparison with a small Moonscape crater.

 Here is a cluster if pie pan craters with the cluster crater from the Blastscape set.
 
I built these years ago but never got beyond the base coat stage.  With all the work I have done on the GW stuff inspired me to finish these up.