I agree , howewever the cost of new is expensive.
On the other hand , a 'cold frame' can be built just out of sahses that have been discarded from someone remodeling, either cheap or free.
A 'Cold Frame', properly positioned to the southern direction , can extend your season by 1 1/2 - 2 months, and uses earth to insulate.
Here in Western New york, the average 'frost line ' is 24 inchess
Recently , the Water Authority announced that this winter's 'frost line' here is 42 inches, almost twice as deep as normal.
We have many home burst pipes , and leakey Water Authority waterlines as a result of this winter .
Cyclical Bear is right, many people get full greenhouses, and then get disenchanted with them
I believe in going cheap , if the occassion arises , and a cold frame meeets my needs.
I hear you, but my interest in a greenhouse is to allow for a 12 month option of growing plants and starting seeds.