Don't know how I missed the post above. :-( Gunz, we are so pleased with the greenhouse kit we bought from turnergreenhouses.com
Ours is 22 by 14 with a plastic cover. We raised it up by about a foot and a half by using cedar logs at the base all around.
The cost for this greenhouse, plus the heater, the fan, automatic temperature control and shade cover, was around $2200.00, if I recall. You simply can't find a greenhouse this size for less unless you design and build it yourself. I know this from all the years I spent researching greenhouses online.
And by the way....the plastic cover was only supposed to last for two years. This is the eighth year it's been on the greenhouse. When it fails, as it eventually will, we can either use polycarbonate panels or throw on another plastic cover. The pre-cut plastic sheets, cut to size, are around $225.00 for our greenhouse if I recall.