The quickest way to acquire experience and salvage in the game is by visiting the Coastal Forest region AFTER you complete the story.
There will be an indefinite amount of deer wandering around in the area and they will re-spawn each time you kill one. Each deer that you kill and loot will earn you 75 experience and 12-15 salvage. The amount will not change no matter how many you kill and loot, so feel free to use it as much as you need in order to purchase the skills and unlock the achievement.
If you farm here before completing the story, there will be a hunting limit enabled, meaning you will not be able to receive as much experience. This is pretty much only for those that have completed the story and are lacking enough experience to purchase all the skills for the achievement.