High tunnels are an inexpensive type of greenhouse that are well-suited for aquaponics. I use a high tunnel to protect my aquaponics system from the elements and to allow year-round growth, even when outdoor temperatures are below freezing.
If you're interested in a greenhouse or high tunnel, I'd suggest getting a kit from Growers Supply. I was referred to them by the manager of a local nursery and have been pleased with them.
Click on the picture below to check out their extensive selection of greenhouses, high tunnels, and supplies. Happy hunting!