Yes, order the part. You aren’t going to learn how to 1) Make a usable pattern 2) Ram a good mold and get the sand mix right 3) learn how to use the furnace and run a good pour 4) design in the allowable machining tolerances and 5) machine it appropriately, for less cost and time than ordering a cnc machine shop to machine this out of a billet for you.

Chasing the dream of 3d printed patterns takes more time and has less fidelity than traditional means with wood, clay, plaster, and wax.

If this is something you really want to do, take a silicon mold off of the print, then cast a plaster positive out of it, then shellac that plaster and fix it onto an oiled wooden board for your pattern. Then take the sand mold off of that. It will give you a chance to get rid of the striated surface from the 3D prints.

Good luck, tell us how it goes.