Export is only $3 get it from places like dollar tree, crazy clarks ect. And super cheap have lots of colours of them. (Sky blue, plum purple, machine grey are good colours.)
Other than that not much is cheap.
We found some places you wouldn't expect to look that have pretty good quality spray paint.(Toy shops that have models that you paint yourself.) And they are really easy to rack from. Some super markers have black and white that is better than export but still expensive but easy to rack. Sometimes they will have chrome.