1. Sourcing ballast from local quary stone dust - sift and free!
2. Table saw (or access to one) to rip loads of scrap wood for trestle bents and retaining walls - be careful!
3. "Wehonest" people from China to fill out a scene - good stuff from Scenic Express up front, these guys in back!
4. Acquarium gravel for loose impedements - Petco on sale!
5. Printing clip art from the web, sanding thin and pasting signs to buildings - Free!
6. Several durable rubber molds and lots of cheap plaster for scenery - Break up plaster rocks and reconfigure!
7. Kitbashing relatively inexpensive HO building kits for big background city scape - Walther cornerstones doubled up to make skyscapers!
8. India ink weathering washes everywhere - one drop goes a long way!
9. 99 cent Home Depot paint returns for sourcing earthy colors - 99 cents!
10. Cardstock models (e.g. Clever!) in strategic places over popups or backgrounds - $<$10 per for a pretty good looking building
11++? What ideas do you have?