I bought my first 100Ah 48V from Sig Solar and paid the feight and duty (ouch). got me started. Is a good battery.
I bought my second 100Ah 48V from Solar Parts Store (got in on the first batch luckily). also a good battery and got me to 200Ahr.
My third battery I built on my own from 280Ahr cells ordered on Alibaba. {pay & pray!} I spent a lot of time finding a supplier and asking for the spec sheets and making sure they were not a reseller of used or old stock getting the total cost shipped to compare with other suppliers etc. these came in three months after order, and all tested perfect (sigh of relief) but I paid more than maybe I should. My Fourth battery is yet to be built, tried another supplier, 280Ahr a bit lower cost but hope to be good cells, due to arrive October 2022.
For me, it is the shipping costs, if you order a heavy item like a server rack battery it costs a ton to ship it here. But if I order Cells, these can be sent at lower cost since they divide them up 2 cells or 4 cells to a box, more boxes but it gets shipped at a lower cost anyway, no truck freight, the courier brings the boxes to your door. Part of the decision to go with 280Ahr cells was the shipping was not a lot more than for 100Ahr cells, but 2.8 x the energy capacity. Building a battery is not for everyone, but my current order is in the $1000 CAD per 100Ahr range for the cell/parts/shipped plus a home made box.