Not a "money pit" more of a money "sponge".
"Mmm, sure have got the beast running fine, ya know, that interior looks a bit tatty, I bet I can get another one pretty cheap, just take a little time to change it out. So THAT'S what the rattle is, let's see, while I've got it apart I could fix this..."
'Tis a slippery slope yer on son! We've all done it and most of us are still doing it.
Owner of a (purchase prices) 1971 $300.00 250C, 1974 $250.00 280C and a 1985 $300.00 500SEL, all mostly restored to the tune of most of my sanity, gad knows how many man hours and no way I'll even compute the parts costs.