For most small urban spaces, the most affordable planter box that still looks good is a simple galvanized steel raised bed or a matte-finish resin self-watering planter. Galvanized steel is usually the better value for patios, rooftops, and community gardens: it is lightweight, weather-resistant, and has a clean industrial look that suits modern balconies. Choose a powder-coated version if you want a softer color and less visible scratching. A small galvanized box is often much cheaper than ceramic, concrete, or hardwood alternatives, yet it still looks intentional rather than temporary.
For a narrow balcony, a UV-resistant resin planter is the most practical budget choice. Look for a matte stone or concrete-look finish, built-in drainage or a self-watering reservoir, and neutral colors such as charcoal, warm gray, or off-white. These details make plastic read as a designed planter rather than a cheap bucket. Avoid very thin, glossy plastic that fades or warps; a slightly thicker resin body usually costs a little more but lasts much longer.
Cedar and fir planter boxes can also be affordable, but the cheapest pine versions often need a liner and a protective finish to last. If your priority is low cost and a natural look, use a simple wooden crate or planter box with a food-safe liner and drainage holes. For food gardening, avoid unknown recycled plastics and make sure there is drainage.
The key is to spend on the features you can see and the ones that affect durability: a clean silhouette, neutral color, drainage, UV resistance, and a size that fits your space. A cheap planter that looks neat, drains well, and survives two or three seasons is a better deal than a trendy box that fails in one year. In short, start with galvanized steel for value and a sharp look, or choose a matte resin self-watering planter for balcony convenience.