That's an excellent and very practical question for anyone living near the ocean! Salt air is incredibly corrosive and can ruin ordinary materials surprisingly fast. For an outdoor trash bin in a coastal area, you really want to avoid standard metals like basic steel or even some powder-coated finishes, as they will rust and pit quickly.
The absolute best material for resisting salt air corrosion is marine-grade stainless steel, specifically Type 316. This alloy contains molybdenum, which gives it superb resistance to chlorides (like salt). It's the same steel used on boat fittings and marine hardware. While it's a premium option, a 316 stainless bin will last for decades with minimal maintenance—just an occasional rinse with fresh water.
A fantastic and often more affordable alternative is high-quality, marine-grade polymer or plastic. Look for bins made from resin plastics like polyethylene that are UV-stabilized and rated for marine environments. These are completely immune to salt corrosion, won't fade badly in the sun, and are very durable. Many modern "coastal lifestyle" bins are made from these robust polymers.
Another good option is powder-coated aluminum. Aluminum naturally forms a protective oxide layer, and a high-quality, thick powder coat adds an extra barrier. Ensure the coating is specifically rated for coastal or marine use. Avoid galvanized steel if possible; while it has a zinc coating, the salt can eventually compromise it, leading to "white rust."
So, in short: for maximum longevity, invest in a 316 stainless steel bin. For great performance at a lower cost, choose a heavy-duty, UV-resistant polymer bin designed for coastal conditions. Your main goal is to avoid any material that will rust, leaving you with a messy, deteriorating eyesore.