Gunite doesn't "just give way" unless something is wrong with it. If it was saturated and froze, the odds are that the part that collapsed is the tip of the iceberg.
I'm going to put your post in the correct section, but I'm also going to tell you that what you need to do is wait till this fall (maybe late summer) and talk to a contractor, once they are no longer so swamped with repairs. You need someone knowledgeable who can actually look at and inspect the pool.
Unfortunately, you're probably right: it won't be cheap.
If you DO want advice from here I have 2 suggestions:
1. Take most advice you might get with a grain of salt: people here are pool owners, not pool builders.
2. Post pictures. You can put them on Picasa, Flickr, Photobucket, and link to them using thebutton.
Good luck!
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