PLEASE NOTE: The method wherein you use the dismantle/create system to create multiple duplicates of items to sell DOESN'T work anymore. After the latest patch, the cost of Alkahest has been increased drastically, making it much less viable. The method I have here works in spades, but it is an END GAME method, meaning that you are going to have to wait until you're just about grinding out the rest of the items to do this, BUT, this method will make your life so much easier in the long run.
Alright, so I am going to try to compress this down as much as I can, but with this method I make about 450k in 10 minutes. It helps immensely with end game costs for Alkahest for completing the item list, as well as getting this achievement without having to worry about it. So, I will create a list of steps you need to follow in order to achieve this.
1) Get the Augment LCK from the Death Trap enemy, and get it to Grade 9, Rank 9. The best place to farm these guys is right outside the warp room in Inferno Caverns.
2) Use your Augment LCK shard to create 9 Augment Gold shards, and once you have created 9, get it to Rank 9 as well. Now, you notice you will have Augment LCK and Augment Gold set as white skill shards which means they're always active.
3) Complete the food side-quests all the way up until you get the Gambler's Ring.
4) Make as many LCK boosting food recipes as you can and eat them.
5) Get you Shard Master achievement (absorb ALL shards). This nets you the Gebel's glasses item from Johannes in his alchemy room
6) Since you have all shards, this means you should have Gebel's glasses, and the Accelerator shard.
Quick addendum: P00R GRENDEL mentions that if you also max the Detective's Eye crystal, it turns into a passive that allows you to collect items from a further distance, making it easier to collect the additional lanterns on the side rooms, while still maintaining your speed!
7) Once you have all of your items, you want to put everything on, and prepare yourself for some serious gold intake.
Below is the exact set-up I use so you can replicate it
Now, once you have your gear, you're all set! What you want to do now is go to the Forbidden Underground Waterway to this room where the crosshair is.
Once there, you'll notice at the bottom of the room that there are three pink torches. What you're going to do is hold down RB to keep Accelerator active, and run in and out of this room from left to right. In the room to the left, you can snag an additional two torches, and one in the room to the right, and you should be getting six torches per run from left to right through these rooms. Just keep on running back and forth and watch your miles turn to gold!
If anyone has any questions or perhaps my solution needs some more info, feel free to inquire or request! Happy trails!