I wasn't specifically grinding to get this achievement, but I just got it yesterday. I think this might be one of the most difficult achievements to get in terms of time/grind required, but I'm underwhelmed by the reward dye: Polished Steel Gray. Oddly, it's not classified as rare, and it's almost identical to Boethiah Gray - just a shade lighter. I was hoping/expecting a very reflective dye (like most of the rare dyes) to make the "classic" shining plate armor look. But it's fairly dull, so... meh. Just a heads up to anyone thinking of pursuing this dye.