Yeah, the cost of the gold may be $50. But the cost to make it more than just the gold. It's also the skilled time of the guy making it, and the cost of other materials used (wax, plaster, etc. for the mold), and amortization of the tools.
I mean, if you just have a plain, unadorned ring, those costs are pretty low. But if it's got interesting designs on it, or is multiple materials, that's going to cause it to be more expensive.
Looking at Zales' website, they've got a 4mm 14K plain men's wedding band for $225. That's probably around 5 grams in weight, with an actual gold content probably around 3 grams. a gram of gold is ~$50 right now, so they're only getting $75 at most in profit from that ring.