The easiest and cheapest way to create a rust texture by JJ Provance
Materials you’ll need
-make up sponges
-testors flat rust
-testors flat brown
Those are the 2 you’ll need but any other natural flat color along with those won’t hurt.

Step 1-rip sponge in half for a better texture dip in paint or drop a small amount on half of the torn side let the paint soak into the sponge don’t dab in globs of paint let the sponge make the texture.

Step 2- after you get a base that you like down you can tear a new sponge or just drop the light brown on top of the rust sponge you already used to mix the colors a bit. The more natural flat colors you use means more texture and realness with the end result just make sure the colors you use would happen in nature naturally. Look at the colors the car was available in and go from there adding a “cheap paint job” over top of the stock color and then sanding down into the original color sometimes adds a cool effect.