There's a useful sticky on this forum by Sailingdog on how to inspect. Check it out. Plenty of books out there too. Casey has a book on inspecting an old boat.
If you are thinking of buying a boat without a marine surveyor--which most, I think, would not recommend--then you need to become fairly expert. The reason that even $3-$6k boats might need a survey is that some problems can potentially eat the complete value of the boat, or even send it below zero. Stuff like wet and rotten deck core, hidden hull damage, marginal standing rigging, blown outboard, etc. can be real expensive.
A marine surveyor can save your butt. And if you want insurance, which might even be required if you plan to keep the boat in a marina, a survey might be required. I believe most consider the size of the boat in their charges--it might not be as much as you think.
2000 Beneteau 331
Northern Chesapeake Bay
Ambition is a poor excuse for not having enough sense to be lazy ~ Steven Wright