You are looking at 10k or more - or a lot of elbow grease to repair.
I did my buddies Catalina 30 with him 2 years ago - power planed off the gel coat - rebuilt, faired, and barrier coated took us about 5 days of work and cost about 1000 bucks in material. I already had the tools. Can't swear to the materials cost, I didn't buy them.
Other than that, personal choice and recommendations of the qualified surveyor etc. etc.
This being the one you were talking about earlier, knock some change off the price and do it if otherwise the boat looks good for the money and the survey says it's good.