Beetle Husk

One kill will not cover it. A full armor set takes several fights, and clearing every recipe in the line takes considerably more, so plan on the golem being a repeat target rather than a one off. He is cheap to resummon and easy to read once you have built the arena, which is what makes the farming bearable.

It comes down to what you already fly with. If you are still on a mid tier pair of wings, take Beetle Wings first, because flight carries further into the lunar events than any set bonus does. If your mobility is already sorted, go straight for the armor and pick the chest piece that matches how you actually fight: Beetle Shell if you expect to eat hits, Beetle Scale Mail if you can stay clean and want the damage.

If you end up with a surplus and want coins, craft the wings and sell those rather than offloading loose husks. The finished item is worth more than the parts that went into it. That does not hold for the armor pieces, where the ingredients are the better sale.