The exact number depends on where you're sitting right now, but if you're not fishing in the random store at all, you might be up against the wall on 4AEQ already.
My dots in the VPB say 1440 light trains to 79 at this point.
But the VPB calculator on that seems to be skipping the final season's 36 TP dump, as running it out manually I'm getting 1548 by light training from here out. 18 trains x 6 BT each = 108, perfectly matching the difference, so I think it's safe to assume it's just not adding in the final offseason dump of TPs.
So if you're not random store fishing, and 100% building the AEQ = 1700 BT (4 x (300+50+75, for +3/+5% items).
1700 - 1548 remaining = you would need to have 152 BT banked or already bought to fully buy all 4 as of today.