That's a great question, and one I considered myself when shopping for a new bin. The price comparison isn't as simple as one always being cheaper. Generally, you'll find that basic plastic outdoor trash cans are significantly less expensive upfront. You can often pick up a standard model for a very budget-friendly price. On the other hand, a comparable-sized metal trash can, typically made from galvanized steel or aluminum, will almost always have a higher initial price tag.
However, focusing solely on the purchase price misses the bigger picture of long-term value. This is where the durability factor comes into play. A well-made metal can is a beast. It resists fading, won't become brittle in the sun, and can handle bumps and weather extremes without cracking. It's also typically more pest-resistant. A plastic can, while sturdy enough, is more susceptible to UV damage over time, which can lead to fading and cracking, especially in harsh climates. It might also be more easily chewed by rodents.
So, while plastic wins on immediate cost savings, metal often proves more cost-effective over many years because it simply lasts longer. Think of it as an investment. If you need a temporary or very low-budget solution, plastic is perfectly fine. But if you want a sturdy, permanent fixture for your patio or backyard that can withstand the elements, the higher initial investment in a metal can is usually worth it. You're paying for decades of reliable service rather than needing a replacement every few seasons.