That's a weird way to look at it. It's not like you're dead for 4-6 years... The start of your PhD is effectively like your working life - albeit a underpaid-but-interesting period. On net my PhD has almost certainly paid off the (ahem) 4-6 year-ish period (ha, ha) that it took me to get a PhD.

Incidentally, 4-6 years is a bit of a wildly optimistic estimate, even if you're not as big a screw-up as I was.