Does a whole garage door need to be replaced if the middle bracket broke?
You can buy most common parts separately. Replace the part rather than have it welded. Ask at your local hardware store (NOT "big-box" store) for a handyman reference, someone familiar with garage doors. Garage door companies will almost always recommend a new door.

Hey, while you are at your local "mom and pop" store, why don't you pick up a few items and help them stay in business?