Second Casey's book. Both "This Old Boat" and his complete book on sailboat maintenance have been invaluable to me.
I bought my C-27 minus a survey. The $5000 didn't justify it and most of the major areas that would cause concern were acceptable. For example, outboard engine so no inboard issues, minimal thru-hulls and all had seacocks, no "Catalina Smile", no evidence of serious leaks, no bulkhead delamination, etc. Only issues of concern was standing rigging (replaced) and needed three new keel nuts (did it myself, thanks Sears!).
Would a survey have helped? Yes, in hindsight. We probably would still have bought the boat. In the end we put about 1.5 times her purchase price into her but the end result is essentially a new boat in all the areas that matter stem to stern, keel to masthead.
It all depends on your tolerance for elbow grease. For me, it was six months of fall, some winter and spring days working on one problem at a time. And we're still working but it is on minor and manageable stuff now.
My next boat will get a survey only due to the monetary outlay involved. For $10K, I'd do it. Below about $7K and depending on your "fix her up" budget, I likely would skip it. An honest owner will tell you what they did and what issues you will have.
Casey also has a good book on surveying fiberglass sailboats. Pick that up if nothing else. You don't need a license to be a surveyor and can do it yourself.
SV South Paw
2000 Hunter 340
South River, MD