The Grow Lab from Everest Garden Supply is the most affordable grow room on the market today.  Just some of the features include:

• Dimensions: 3'11" x 3'11" x 6'7"
• Clear viewing windows!
  on most models (currently GL80, GL120 & GL145; other models to follow)
• Increased weight capacity
  roof cross-members easily support 100 pounds
• Sturdy powder coated framework
  helps protect against rust and gives a cleaner look; thicker than previous models
• Highly reflective interior
  significant increase in reflectivity for improved lighting performance
• Thermally protected
  tent material reflects 97% of all radiant heat for superior insulation
• Completely non-toxic
  will not react under light and heat, and no off-gassing to harm plants
• Improved fabric & zippers
  thicker fabric than previous models, with the best zippers on the market
• Moveable roof cross-members
  easily adjust lighting and accessories; pieces snap into desired place for better functionality
• Multiple intake/exhaust ports
  including two ports opposite each other at reflector level for air-cooling of lighting system on most models
• Adjustable fan and ducting attachments
  no more clamps or reducers needed!
• Waterproof floor
  a second floor that is removable for easy cleaning between crops