Here are a few ideas for cheap greenhouses that can be put together in a day or two: 1. simple pallet greenhouse. the simplest and most inexpensive greenhouse can be made with a few old pallets. it may not accommodate a whole lot of plants, but can offer a warm home to a few precious ones over the winter.. Garden greenhouse made from recycled pallets, perfect to grow your aromatic plants. #garden #palletplanters #recyclingwoodpallets. How i built a pallet greenhouse with a rain gutter grow system. i built a pallet greenhouse and use the rain gutter grow system for watering. 2 5# box of 2