Not a day goes by that I don't see people here coming up with creative ideas. Considering the length of time many here have been in the hobby and the number of layouts we've all built, I'd imagine there are a lot of innovative solutions out there that don't involve a significant investment. Making ties with Popsicle sticks, using zip bands to secure track, cat litter for ballast, etc...
What's something you do or have done with your trains/layout that costs less than $10 but adds a lot in either looks or performance?
Here's my contribution... every time I purchase a hopper with a coal load, I spray the (usually shiny) load flat black, and it immediately adds some depth. I've done dozens of cars with one can, so less than three dollars invested.