The best numbers I got for an early 1970s Trojan 30 are from NADA which lists a low to avg retail of $5950 to $7150 for a 1974 Trojan 30' sea raider, the oldest year for which they list a 30 foot Trojan. This is based on a single 280 hp engine. You said you have twins so your milage may vary. That is 3 years newer, but with no trailer. Take it for what you may.
Now here's my story. Two years ago I bougt a 1975 Trojan F26 with a Chrysler 318 FWC with 800 hours for just under $5,000. The cockpit deck was rotted out. the Hull was and still is in amazing condition for her age. Stringers are solid, which is crucial. Two years later I've spent about another $10,000 on equipment lumber, fiberglass, electronics, marine hardware, and a rebuilt engine. I did almost all the work myself. I did pay a mechanic friend to help me with the rebuilt engine. My project list goes something like this:
2004
removed rotted cockpit deck and frames, rebuilt framing and replaced deck with mahogany planks over marine plywood. (added more & larger hatches for improved access below deck for engine maintenance)
rebuilt main cabin bulkhead below cockpit deck due to rot
Replaced water damaged cockpit liner (original was like formica on pressboard)
Installed new alternator & starter
Stripped and refinished teak cockpit trim & main cabin bulkhead.
Installed new aluminum fuel tank, fuel filler hose
Rebuilt fuel tank mounting bed.
added secondary fuse panel. Removed & replaced shoddy after market wiring installed by previous owners.
Removed original water tank to improve engine access
Installed new head, holding tank & all associated plumbing
Installed new 20 gal plastic water tank & replaced all hoses (relocated tank forward of original location under hanging locker) Included outlet for fresh water washdown.
Installed salt water washdown pump & outlet
Replaced 2 batteries (including new battery boxes)
New VHF radio
Replaced steering cable
Installed new bilge pump & float switch
Replaced engine cooling seacock & intake hoses
Reupholsterd captain and mate seats
Welded damaged swim platform mounting brackets. Stripped & refinished teak swim platform (new stainless mounting bolts).
Tightened up bimini cover frame & Fabric - replaced misc. hardware. Re-sticthed bad seams.
2005
Replaced engine (from 1986) with factory remanufactured 318 & new velet drive transmission. (rebuilt distributor and carburetor from previous engine)
Replaced rusted engine mounts.
New engine temperature guage and oil pressure guage.
Upgraded rudder & extended keel by 6" to improve tracking stabilty
Stripped 30+ years of bottom paint to gel coat.
Replaced propeller shaft
Reconditioned propeller
New depth sounder (with transom mounted transducer)
Replaced failed fresh water pressure pump.
Re-wired trim tabs
Upgraded transmission oil cooler
What I still have to go.....
The aluminum windsheild could use re-finishing.
The cabin floor has some sponginess and needs to be rebuilt in places.
Most of the interior teak is in good condition, but various hinges need replacing, the walls in the head need to be re-finished. They just have a coat of paint now.
What I have now, is a 30+ year old boat with most of its mechanical systems replaced, and still a fair amount of cosmetic improvements needed on the interior. It took me most of the summer to work out mechanical bugs with the rebuilt engine, which was a little more than I bargained for, but I'm looking forward to next season. Considering the time I put in, I don't think that I'm much ahead financially of where I would have been if I'd just spent a bit more on a newer boat, but I fel like I know every screw, wire, belt and hose with my eyes closed. With two kids in college, and another headed that way, spending $65-90K, on a newer boat that size is out of the question for me, but I've seen some pretty nice used rigs advertised for $20-30k.
Offshore dreams said if you don't keep it a long time, its a bad investment, but I don't quite agree with that. A boat is not an investment. It is an expense. If you want an investment, consider a mutual fund or real estate, not a boat. One more thought. I got my rebuilt engine running good late in the summer just a couple of weeks before marine fuel went over $4.00/gallon.
If you love being on the water, and don't mind crawling around in tight spaces trying to fix somthing that was installed before the deck was put in place, then there is nothing finer than simply messing around in boats.

Good Luck!