Walmart with Backyard Discovery has the well-reviewed Backyard Discovery Zalie 11' x 7' Cedar Wood Greenhouse Kit on sale for $2499 with free shipping. Also at Amazon, but limited stock. The 9' x 6' kit is also on sale for $1799. 

• 86 square feet of interior space / 23 linear feet of foldable and fixed staging shelves
• 3 electrical outlets and 3 USB ports, 2 easy-open windows, exterior and interior hose hook-ups
• Withstands up to 4,400 pounds or 30 inches of snow load, and winds up to 100 mph