Previous products took much longer for batches to sell out. Even the AMD framework 13 laptops didn't sell this fast and they were the #1 thing the community had been asking for for about a year.
We (sadly) can't tell how many units are in a batch. But we can tell that demand is far exceeding their expectations.
I think the DIY model doesn't include some components in the base price and that is why it is cheaper. Once you configure it to include other components it is a comparable price.
It seems the DIY option will only really save you money if you already have those components or if you buy those other components cheaply somewhere else.