With this in mind, I made some custom bases cheaply and easily and wanted to share how.
This stuff was the key. Picked it up from a local craft store for about $15.
Then you take the bases you want to copy, adhere them to a slick surface (I used greenstuff and laquered plywood) and cover them with a thin layer. My first attempt was too thick:
It should be much thinner than that.
Once it dries (should be almost clear) repeat for about 10-15 times. Your brush will get pretty messed up, so use a cheap one:
Also, make sure you do this in a well ventilated area.
After the bases are completely covered, peel off the rubber and trim the edges. Then take some putty (I used FIMO but greenstuff works as well) and use your mold to create a new base or base topper (I went with the latter to save putty).
Here is the finished result, awaiting painting!: