At least 75% of the classic cars located are "rare" and "worth a lot of money". Even if they're not. If the car is in original condition and was only driven for 10 years, it should have low original miles. If the "rust" is body cancer, that would lower the value. If it's just surface rust then it's not a real problem. Hagerty Insurance can give you a rough estimate of it's insured value. Any modifications/upgrades would detract from it's "restorable" value. My '66 (in fair condition) carries a value of $7k but restored (no modifications) up to $27k. If I upgraded to OEM 289 engine the value would top out at $35.