Get the survey. We had close friends that accepted delivery of a quite expensive new boat without one and they had all kinds of problems which took 3 years and lots of lawyers to resolve. The survey would easily have discovered the issues and they would not have taken posession.
will give you a good idea of the detail in a survey and you can click on the rates link as well.
In my experience, most sailboat surveyors don't do a very good job on engine analysis and I would recommend a diesel guy also be brought in to check engine performance in an older boat. Some folks also do an oil analysis on older engines but I personally would only do this if the diesel guy suggested it.
Most insurance companies and loan companies will want to see a survey on any boat that is not a factory purchase.
Aside from new boats, I will also say that every survey I've had done over the years has saved me more $$ in purchase price than the cost of the survey.