In the Olympics, Bronze, Silver and Gold medals are awarded. All these metals have alloys that work best for casting, machining, die-striking, etc. If you want to cast a bronze metal, the silicon bronze alloys like Everdur have a lot to recommend them; they cast very cleanly, with little damage from gas inclusion and are easy to weld, since compatible rods are available. But “ancient bronze”, an alloy of copper and tin, also casts well and has a lot of history going for it.
The same cannot be said for brass, a more modern alloy of copper and zinc. When you melt it, it immediately starts emitting a dense toxic white smoke. A heavy layer of flux will slow but not stop this reaction. Zinc has a very strong tendency to combine with oxygen and form zinc oxide (the stuff lifeguards traditionally slather on around their eyes to retard sunburn). The process of forming this material also can cause gas bubbles to form inside the cooling metal mass of your medal. It might show itself right away, or it could wait until you remove a little metal from the surface to reveal a big black hole.
Perhaps that’s why nobody awards their winners a Brass Medal. The difference in the price of the metal pales into insignificance when you figure in the failure rate. You can save money using cheaper metals if you’re producing something in large volumes and you can spend some time tweaking the process until it works reliably. But if you’re just trying to make one - or even a few - of these things, use bronze, not brass. It sounds more expensive and you’ll get paid more for using it.