I just answered another similar post inquiry about a 1980 C 30, & U may find this advice helpful: as I also have a 1980 C 30.
I paid around $9500 for mine, & if the boat has never had
any significant upgrades or refit that's about what she's worth.
As a comparison though, My C 30 seller was kinda desperate to sell, being transferred across country. Her loss was my gain as the previous owner has installed new UK Halsey sails, new electrical panel, rebuilt diesel, wheel steering & a host of upgrades. The cabin looked tired, & she needed a haul out, which gave me the ammunition to get the price down. Remember that most boats that have been sitting in a slip for 2-3 years are in need of a haul out to clean & repaint the bottom. You cannot perform a decent haul out & bottom job for less then about a grand. It also makes it a lot easier to determine the condition of the keel join to inspect for the Catalina smile separation crack which is common. Also inspect the condition of the rudder tube & bearing for excessive play or damage from groundings, etc.
I always recommend to new prospective buyers to buy a copy of Don Casey's "Inspecting the Aging Sailboat" which has an invaluable lists of items that need to be checked that the novice will never think of. Take a rubber hammer with U to sound out decks for delamination around deck fittings. Take a good flashlight to inspect the engine, trans, bilge post for rot, thru hull fittings & tanks for corrosion. etc. I work as a professional building inspector, & my number one tool are a flashlight & my eyes & ears. Good luck on the hunt, one of my favorite endeavors.
If you are not familiar with sailboats, then by all means hire a surveyor. But they are expensive, & the book I mentioned will help U weed out the bad apples. I personally would not want a boat with tiller steering, as I'm getting older & a 30 ft. boat with a tiller will break your arm trying to steer a beamy boat like a C30 after on hour. I used to have a C 25 with tiller & a C 22 as well, it was tiring. Wheel steering is a huge improvement, but an expensive upgrade. Get a C 30 already upgraded.
Lastly, the Atomic 4 is a venerable & durable engine, but is getting up there in age. (Although so is a 1980 boat!) An Atomic 4 will lower the value of the boat (& raise your insurance premiums) when compared to the same model with a diesel.
But that may get U to the price U need. I know I will take flak for this, but in 30 years of owning & sailing boats there are code words that I avoid like the plague when reading boat ads: "Atomic 4 still runs, classic or original, needs a lil work, fixer upper, or just don't have time to sail her anymore." These have always been code words for "neglected or abused, out of date, never updated since built, money pit."
Sometimes its worth paying a lil more to get a boat in better condition.
I like the old adage that I'd rather sail then sand. That's why I avoid wooden boats & reg. gas engines that are more then 30 years old.
Good luck on the hunt.