I've seen plastic type ones in Koctas. They are either like a small wardrobe or a trunk type. Don't know how much they are though. They seem quite sturdy, but I thought they were expensive (sorry can't remember prices). You could always have a look on Koctas website.
We purchased an upright grey sturdy plastic cupboard for outside from Koc Tac in ~January they are the same as the ones they sell in uk for storing shed type contents. We keep gardening tools and paint (nothing of v alue though) in ours. Can't remember the cost , the receipt is back in Turkey. If they're not available now they definitely are in the winter.
The nearest one is Kusadasi I think. Ive had one made for my terrace, mine is quite big.
Im not sure how to add a photo to a reply. If youd like more details on mine i can email you the pics and price etc.