Home Depot?Most folks I have seen posting build their own. Only way around that I have seen are Geohex or similar 3D printed terrain.
Geohex on Ebay is probably your best source for a turnkey terrain system.The new hotness is 3D printing terrain and painting/flocking. That removes the tedious work of hotwiring foam insulation at least. If that's a workload more up your alley, I could recommend... I think they're called Thunderhead studios. Heavy up-front investment if you don't want to buy/ship the plastic objects themselves. I just got a 3D printer for about $300. Spools of plastic are about $15-25 depending on color/type, about like inkjet cartridges. There's also bespoke services. I know Greatsarcasmo runs his own small shop and will do some on-demand printing.
Steel Warrior Studios has Hills you can either buy, or the .stl files to print your own.Otherwise, yeah, Home Depot, a sharp knife, and green paint.
Cannot recommend enough Thunderhead...I have a LOT of his files,
Were are those hills I can't seem to find them
Tell you a funny story about a sharp knife. Many years ago me and my wife were making some cheap hills out of cheap phone. My wife started making fun of the box cutter she was using slipped and cut her finger to the bone. She know has a health respect for box cutters. I know they are easy make....Just don't want to will probally break down and just make them