You may need to buy the expensive model railroad paints for painting locomotives and rolling stock, because you need railroad colors, but for everything else on the railroad, you can pick out the inexpensive craft paints at craft stores. I volunteer at a children's church camp in the nearby mountains. I'm in charge of the craft program at the camp, and we have found the the least expensive paint to use is acryllic house paint. We buy as close to pure color as we can get for primary colors, and then mix many of our other colors from the primary colors. We tried to make orange from our red and yellow one year and kept getting a "peach" color. Either the red or the yellow had white in it, so I bought a gallon of the most orange color I could get at the local Home Depot. I bet the guy mixing paint at the store wondered who was painting a house bright orange!