I have both the Bellpoint from getting the 7-11 set and the ABD. I'm far from getting 100 million bells in savings, but I got the 7-11 set and the ABD from extremely generous people on here
I earned one legitimately back in January. I say legitimately because although I had a friend give me an ABD prior to that, it was from someone that duped them.
I set out for an ABD halfway throughout my game, which took me ~10-11 weeks to earn.
I bought and sold turnips, took up all of my locker spaces and made somewhere from 8-12 mil per week
I got mine in September or October, so it took me approx 14/15 months to save 100 million bells. I had gotten up to 70 million, and then I decided to sell some tbt for in-game bells to get the last lot, as I really wanted my gold savers badge.
I only got them from trades. The last item I got from the post office was the safe, and that was just because I was holding someone's bells while they reset their town. lol
I've been playing since release and still don't have it. I got the safe last week. I'm playing the stalk market now, so I hope to get it within a few months. We'll see.