So here's an easy tip: Buy your diamonds at /warp station13 as soon as they are able to restock them for 26$ each. Then, go sell those diamonds for 26.50$ at /warp station22 for a .50$ profit per diamond. Station22's diamond sell sign has over 80k$ in its diamond sell sign, so the sign wont run out of stock too quickly, but station 13 is currently out of stocks on the diamond buy sign. Hope this helps :)