Kyle, to answer your question. I would go on You Tube and try and watch as many videos as you can on weathering. There are many techniques and many use combinations of both airbrushing, artist tube acrylics and powders. One of the best I’ve seen on a freight car tutorial was Boomer Diorama on You Tube. An HO modeler but he did an o scale boxcar.
Cost is going to be around $100 whether you go for an airbrush or weathering powders such as Pan Pastels and artists acrylics. A bit more if you also need a air compressor. While it’s nice to have a huge assortment of colors. You can get started with 4 or 5.
Practice on some inexpensive cars you have no attachment to get the feel of how much to apply. Once you get your technique down move on to your prized rolling stock and engines. Weathering is designed to make the details pop so that you notice them. From my experience. It’s easier to get consistent results on say an Atlas Master series car than a simple car with molded in details.
