stangcoupe1970

I'm working on getting the car able to drive in the cold weather, I was going to get a new blower motor and heater core. I went to get the heater box out of the car and I gave it a light tug to see how it was held on, and the entire box broke off the firewall and I was sitting in the car stunned thinking a replacement was hard to come by. turns out they aren't but they are expensive.

So is there a way I can repair the one I have or is there a replacement that isn't expensive?