Let me preface what I am about to say with the statement that I am by no means rich. I started this hobby this past February with very small volume. I am currently at a 16 box weekly order of halves. At one point, my weekly orders were up to the 20-30 box range and I actually did a high week of 36 boxes over this past Christmas. There is definitely a minimum amount of bankroll required to do some volume, but really it is only $500 so that you can order a box. Regardless of what my financial situation looks like on any given week money is always a much smaller constraint on this hobby than time is. If I had a reasonable amount of time on my hands and a $500 bankroll I could do at least 6 boxes a week. You just have to structure your orders in such a way that you are never getting more boxes at more banks than you have time to dump the previous pickups in order to pick up the next orders. I'm not sure if that last sentence makes sense.
The summary version is: I think time and bankroll are actually a ratio that determines the amount of volume you can hunt. If I didn't have a job, I could probably search 20 boxes a week with a $500 bank roll because I would have the time every day to go to a bunch of different banks and pickup one box at each bank and search and dump along the way all day. Since I'm working 50-60 hours a week right now, the only way to continue searching my current volume is to have a larger bankroll to account for the lack of time that I have. This way I can pick up larger quantities of boxes at each bank at various points in the week and concentrate all of my dumps in one or two dump days in the week. See what I mean? Since I don't have as much time I can account for that lack of time by dumping $4-6k in halves at one stop or two rather than making 8-12 dump stops of $500 each.
But really, if you can make the sacrifice in terms of time over the short term to account for a smaller bankroll your finds should increase relatively quickly which should allow you to sell some finds and up your bankroll which then allows you to choose whether you want to keep sacrificing time or up your bankroll. Or a third option is to stay with the low volume if you are happy with that. There's nothing wrong with being in the minors. It's just a little less efficient in terms of ROI.