You can also rent anime by mail from Netflix just like back then, assuming you live in the US, which I realize does not count as "watching anime online" but it solves the problem of watching Gundam, Gundam 08 MS Team, or Outlaw Star without going to an illegal site or purchasing the DVDs.
A problem you might notice is that legal streaming sites don't have a good collection of older anime at all. You won't find most anime you want to watch streaming legally, because streaming sites focus on newer anime for more viewership, and those licenses may expire after a couple of years anyways. So it would be difficult to find anime before 2011 that catches your attention, or any anime movie for that matter.
I don't know, maybe that's too inconvenient, but it's an option, and in terms of cost it beats spending money on boxed sets.