That is a rediculous and price gouging.
You can pull the whole unit from one in the junk yard for around $60. then you get the blower motor, evaporater and heater core, plus vac pods etc... and you get the experience of pulling the dash.
I haven`t worked on the 126 ac/heat box but have pulled a few 123 units so that is unchartered waters for me.
I saw a plastic welding kit a while back. maybe you could repair the flap?
Charlie