I bought some cheap garden shelves for pot plants like these ones
https://i.ebayimg.com/images/g/UCMAAOSwarFgLlOn/s-l500.jpg
a couple of years ago. The metal pipes are rusting through and falling apart. From I've read on the web, similar shelves and greenhouses made with the same 16mm green, powder coated steel rust through and don't last more than a couple of years if they are exposed to the elements.
Can anybody suggest a better product for a reasonable price? I've seen the galvanised ones that plant nurseries use for sale but they are way too expensive.
plastic would probably be a good option, though it won't be as strong. wood will likely fare worse than the steel.
how expensive? think of the cost long term, if the ones that plant nurseries use last, it might be worth it even if it is expensive. you're always going to be compromising if you want cheap stuff, whether it's durability, lifespan or strength