Hard to tell without pictures...
Is the lead attached to a fibreglass keel "stub" (external lead ballast)? If so - it may not be too big an issue. If it is lead poured into a moulded fibreglas keel (an encapsulated keel) it is going to be a bit more diffcult and expensive to deal with. I'm going to suggest that if it is encapsulated, you might want to look for a new boat, because you're probably going to end up way over budget fixing it AND the interior.
Let's be optimistic and assume it's external
First thing you want to do is get the boat out of the water. I wouldn't wait any longer than necessary. When it's on the cradle, let it dry out for a week or so. Then you want to drop the keel about an inch. Loosen the keel boats AFTER you have rigged up some support - or lift the boat a little but again - support it as close to the keel stub (sump) as possible. Check the keel bolts for wear, (replace them if necessary/possible). Clean out all the old bedding material on the sump and the top of the ballast casting (the lead). If there is any corrosion or wear, on either surface, fill it and fair it as well as you can.
Also, look carefully at the holes that your keel bolts go through. Does it look like there has been any wear there ? (One of those little mirrors like the dentists use is good for this) Typically, the lateral stress on the keel will enlarge the lower portion of the keel bolt aperture slightly, inversely proportinate to the length of the sump. If there is appreciable wear there, it's a good idea to try to fill it a bit.
I do it this way, but there are thousands who will disagree with me. I mix up a little slow-setting epoxy and add some silica to make it into a putty. THen I spray the bolt and the hole with 3M Silicone lubricant and then try to stick minute amounts of the putty into the bolt hole with a small rod or flat-head screwdriver. Not sure if this really does anything but it makes me feel like I have tried...
Now pick your favorite bedding compound - I like 3M 5200 but other people may suggest a different product - put a whole lot in the joint and drop the boat back on to the ballast. Tighten your keel bolts BEFORE the epoxy has a chance to harden. Let it sit for a few days to give the bedding a chance to set up a bit.
You should now have a boat with a watertight hull/keel joint that requires a straight-forward fibreglass repair job. Get rid of all the loose stuff, fair off the rest on a really shallow angle. Seal the exposed metal with something like S1 sealer, then apply a layer of mat, wet it out and roll it smooth. Use the correct fibreglass roller that removes air bubbles - not a paint roller.
Let this cure and then keep filling and fairing until you're ready to paint.
If your keel is encapsulated lead, you are going to need to let the boat dry out for quite a bit longer, until you are sure it is perfectly dry inside the keel. Then you need to rebuild the fibreglass sheathing around the lead. This needs to be well-bonded to the existing sheathing, as it's what holds the lead in place.
Once you have done this, it might be a good idea to pour as much epoxy into the cavity as you can to seal the metal and hold it in place. Do this bit by bit though, to allow air bubbles to work their way out.
I don't know what yards in your area charge, but up here, I'd expect the above work to cost me between one and four thousand dollars - depending on how much travel-lift time it required.
You may find that your encapsulated keel is only one third lead and two thirds foam-filled fibreglass, or something similar, in which case you're going to have to repair the capsule, then secure the ballast, then dig out the foam and replace it as well.
At that point - I'd be tempted to just fill the whole thing with epoxy mixed with rags and old screwdrivers and sell it to someone who wasn't too concerned about buying a finely balanced boat - but have the decency to let them know what they're buying of course.
Good luck !
The next thing is to look carefully at the