Guild Wars 2

Quickest (not necessarily cheapest) way for 2000 Commendations in one go would be 3 Lv75-80 exotic trinkets (amulet/ring/earring).

Candy Corn Orichalcum Amulet seems to be the cheapest, although Opal Orbs shot up in price. But still one of the best methods if you want those rewards quick.

If you think buying Black Lion Keys with commendations is not worth it, then you are tossing the wrong items into the forge. Three Godskull weapons craft at ~6s each for the cheapest ones. Total cost of the three items and packaging ~17s. You get 70 commendations in return, giving an exchange rate of ~24c/commendation. A key costs 285 commendations for a total cost of ~70s. This is far cheaper than the cost at the current exchange rate with gems.

I did the calculation and I knew it is not worth in term of cost. However, those 250x or 500x harvesting/mining tools are good to save your bag space and time to replenish them if you mine/harvest a lot. And now that they are account bound, I think it is worth to get them.