Here is a small greenhouse from Harbor Freight Tools, 6 x 8 ft for $300. There are some other inexpensive models from Amazon ($500, Palram Mythos http://www.amazon.com/Palram-Mythos-6-Feet-8-Feet-Greenhouse/dp/B004HR1VFA) and Coscto ($700) but they cost more.
- use 20% off coupon to buy the greenhouse from Harbor Freight Tools (search Google for the coupon) and (http://www.harborfreight.com/20off-coupon912-aff-17547.html)
- shipment of the greenhouse from Harbor Freight Tools costs $97, so it is worthwhile to call if the greenhouse is available at the local sore (http://www.harborfreight.com//storelocator/location/map)
- use tape to waterproof the panels (http://www.homedepot.com/p/t/100030120)
- building a wooden frame (anchored with concrete) is recommended
Search Google for improvements to find suggestions.
Video of improvements: http://www.youtube.com/watch?v=Q6DpjzaIJ8A and http://www.youtube.com/watch?v=axxa_QrRrpE -- More here: http://www.youtube.com/user/Nepenthesis/videos
Building and Improving the Harbor Freight 6x8 Greenhouse: http://www.instructables.com/id/Building-and-Improving-the-Harbor-Freight-6x8-Gree/
Videos from GrowingYourGreens:
How to make a small greenhouse out of five pieces of plastic pipe, a plastic painter's drop cloth, some zip ties and a few bricks: DIY Instant Greenhouse For Under $20 - YouTube http://bit.ly/19m4jHf