Michaels craft store. What I found were several good ideas that could be used to cheaply augment a Frugal GM's table.
I'm sure there are probably a ton more ideas/products available in the store, but here were three that jumped out at me.
The first thing I found was this bag of moss foliage. Pretty inane stuff I realize, but if you make your own trees, this moss is perfect for just such an endeavor. At the model hobby store a bag goes for $15-$20, but at Michaels it is only $6. For $6 you could afford to get several bags in order to mix & match you get a good blend of colors on your trees. Trees are rarely a solid color, but the bags of foliage mix are just that. In order to get a blend of colors using moss from traditional gamer hobby stores you'd have to spend $50+.