This Achievment is one of the glitched ones. Make sure you save the game befor you spend your money.
If it does not unlock, clear persistent storage and restart the game.
For this achivement you have to spend money on improving the house the dutchess gifts to you (this happens after a few mainline story missions).
1. Unlock the estate by playing the DLCs main storyline. This will trigger a secondary questline.
2. Save 14k coins.
3. Create a savefile in front of the Majordomo (Housekeeper).
4. Choose every possible option to spend money. Then meditate for 3 days, better go for 3.5 days since its a little glitchy sometimes.
5. Head to the lower areas of the estate to unreaval an alchemie laboratory. Its straight down the hallway. Blow up the wall with Aard, then head back out.
6. Get back to the Majordomo and repeat step 5.
7. Your achievment should unlock, but might need a little interaction with the Majordomo.
8. Reload the save you created on Step3, if you want to keep your money or spend it elsewhere.