(EDIT: Not true, see below.)
(EDIT: Not true, see below.)
Searching for "Vanguard S&P mutual fund minimum 1993" shows that many had a minimum of 3000? I'm guessing that is the same general search you were doing?
I'm torn, as I want to think this isn't wrong. However, I also remember you could buy a car for 10k EASY in the early nineties. Was a pretty decent sum to make in a year. Especially if it was on top of all other expenses. I'd also hazard that for many, getting a car to commute to a job would have probably been a better investment. (Of course... this is only true if you use the car for the added productivity.)
Massive kudos to your dad for getting you to do this!
According to https://corporate.vanguard.com/content/corporatesite/us/en/c... they were 0.35% in 1990. Higher than now, but hardly "high".
Of course there are other fees involved and everything was more complex and more expensive.