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I would be interested to know what their proposed method of repair would be. And perhaps my advice would be to get a second opinion/quotation.
Is the sump weak so that the keel wobbles or flexes? Is the bottom of the bulkhead still bonded to the hull? (Just trying to figure out what happened and hoping that my boat isn't susceptible.)
Not saying that this is directly relevant to your problem, but it might be. I once considered adopting a boat that had developed keel wobble, but it had an external bolted-on keel. My plan (following others with the same model) was going to involve building a grid of stringers and floors to stiffen the sump area, incorporating a new backing plate for the keel and installing new longer keel bolts to bind it all together. But 1. That was only the first of this boats problems and 2. It would have reduced the headroom in the cabin below my tolerance. Better boats were available for less effort. (And that boat had no sole to be cut out of the way, either.)
(The PO's solution, BTW, was to pour the sump full of epoxy. Yes, over the keel bolts and everything.

Didn't work. Just left another mess for someone to clean up.)
Depending on what the quote for the "right" repair is, some options to consider might be.
1. Do a "patch" repair and enjoy the boat for as long as it lasts.
2. Haul it to your back yard and do the project yourself at much less cost (but loss of the boat for a season.)
3. Make a lateral move to another boat for less money.