Theres a company I found that sell's rebuilt GM columns with or without a core exchange... IIRC a rebuilt column was like $800-$900 not including the core charge or shipping, one of the reasons I chose to restore my own.
Rebuilding a column is a fairly involved project but it can be done with basic tools for the most part, lock plate tools and tilt pin pullers are rather cheap. I think I spent about $150 in parts to do the whole thing: new lock cylinder (with GM keys), new ignition rack, ignition switch, neutral safety switch, turn signal switch, rubber flange gasket, some grease, loctite, and a few cans of paint. I just cleaned and reused everything else, I almost had to buy the upper bearing kit because the ball bearings got knocked all over the floor but I was able to find them all.
Theres a few Youtube videos on the process.
Note: If you choose to rebuild don't cut the rubber flange that seals it to the firewall off like I did, they're a PIA to find replacements for.
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