You can get a double poly overwintering structure for less than $2,000.
Would be called by some a cold-frame.
Real galvanized tube frame, not pvc or chincy steel. Basically the same components of a full-size greenhouse, just not as tall or long and wide.
See:
https://www.farmtek.com/farm/supplie...;pg103108.html
http://store.rimolgreenhouses.com/Ca...8_p/cm1548.htm