Hi all,

First the good:
I've recently come into ownership of a 1974 450-SEL with the 4.5L v8.
Car has 77k miles on it, and ran perfectly until it was parked.

Now onto the bad:
Car has sat for 5 years. Only rust is a small spot in the trunk where the drain plug used to be and some visible rust on the corner of the radiator.
All the rubber in the car is probably shot, as are the tires. Other than that not sure.

I'm trying to decide if I should dump $ into it and restore it to keep as an around-town family car or if I should just let it go to someone who wants to fix it up. I'm moderately mechanically inclined, and would be comfortable doing most of the work myself.

The family mentioned they had an estimate done a couple years back and were told 5k, but they had no breakdown of parts/labor or what the mechanic said needed to be done.

Anyone want to field a guess about how much I'd have to dump into it to get it running, assuming all that needed to be done was fluids/rubber/anything else to replace after sitting for 5 years?

No one can answer that but you. The car is certainly not an investment. Either assign hobby status to a restoration or sell it to someone who will.