You also unfortunately asked the wrong time of year . . . Hobby Lobby and other craft stores put little wire/brush trees- some with snow- for sale really cheap after Christmas . . . sometimes right before Christmas. I got some of mine that way. You can also go, at least at Hobby Lobby, when they put fake/plastic plants on sale . . . I got some mixed little frond and pine-cone thing that each snaps off the base and they are the perfect height for BT trees to the mechs. I am thinking of painting leave/fronds exotic colors for 'alien' trees.
Again, seeking some exotic I ordered some aquarium plants from a big online store.
Smoothedo-Pets Aquarium Plants Fish Tank Decorations 20pcs Small Size/1inch Tall Plastic Artificial Plant Goldfish Waterscape Fish Hides Mini Grass Set (Purple)
Smoothedo-Pets Aquarium Plants Fish Tank Decorations 20pcs Small Size/1inch Tall Plastic Artificial Plant Goldfish Waterscape Fish Hides Mini Grass Set (Green-C)
Eachof the above cost me about $.40 a plant when I bought them a little under a year and a half ago, and b/c of the round black heavy plastic they serve as excellent weights on green hexes used to denote the actual wood hexes which is different than the model railroad trees that are 'top' heavy. The purple is pretty vibrant so it pops on the map the few times I have used one. I painted the black green and I thought about flocking it but that would make it look different than the green plastic portion. I have thought about spraying it with adhesive and then dumping flocking on it to get a 'fuzzy' tree as well, like some of the trees carefully trimmed to keep their branches close. Also snagged a grass square 'lawn' which I will detach from the mat to add to the trees.
BUT . . . realize that across the world there have been some really interesting things done with shrubbery that could give your table some variety AND help stabilize trees.
This tree follows a older English fashion of tying down, or 'grounding' trees, the first two are from Castle Malahide, the other is one I found for examples. It basically gives you green from the tree from ground to crown though the 2nd photo shows they did not keep up with that sort of tree and it is different than the oak. You COULD make 1 hex of impassible terrain with branches over and touching the ground, a 'mech tunnel' in the greenery of the forest . . . always wondered what a firefight among sequoias would look like on the table.