Have you considered a "poly-tunnel"?
These greenhouses are inexpensive. Made of heavy duty polythene and only a basic frame covered with the polythene sheet. They are easy to construct, fix the support hoops into the ground a little like an ingloo, cover with poly sheet and add your plants.
They are also easy to move around and disassembel when you are not using them.
For growing small quantities of plants, cloches work well too. These are miniature greenhouses which cover a small number of plants.