I need to dye my coveralls.... help?

I’ve had a pair of Big Mac charcoal coveralls for the past 12 years that have served me well! but they still just look too… I dunno… clean. they may have faded just a shade too. so what is the best, easiest, and possibly cheapest way to get them looking the way they should?

I used RIT dye on mine but I always look for bargains and buy Big macs that are way different styles/colors and bleach then dye em the color I want. Just bought a pair tonight but i,m tall and that makes em even rarer 2 find.