So, a friend and I discovered what has to be the absolute easiest way to get this achievement. Is completely doable solo, of course the only concern are other players coming after you. I managed to get into a game solo.
Go to the town of Escalera in the bottom left of the map. At the top of a hill is a hacienda/mansion. Go through the gates, on the front corner of the wall is a tower with a ladder going up into it. Climb up here and take cover against a wall. Now, start shooting the law officers in the area and keep doing it until you receive $1000 Bounty / Public Enemy status. Now just sit here for 10 min. Occasionally a guard will try the ladder, so you need to watch that, but that's all.
Now the best part...typically you have to escape to get the achievement, but for some reason, because they can't see you on top of the tower, after a few moments you'll lose your wanted status and the achievement will pop.
In summary, climb tower, become public enemy, wait 10 min. Done.