It would cost about $3 to make the 2GB RPI5 a 4GB PI5, and you might save something close to that by removing a SKU. You then get a bunch of new applications (which need more RAM) for your SBC and your product sells more as it looks better value. On the whole that $3 is now looking like a bargin.
I don't think 32GB is needed or sensible, so will disagree there.
32GB is impossible at present. No-one makes a 256 gigabit (32x8) chip to fit in the same footprint, so then you have to do a new board design to support multiple chips, which might not be doable in the board's current footprint.
Micron do a 192 gigabit (=24GB) chip but it's LPDDR5, rather than LPDDR4x, which I imagine the RPi 5's SoC can't drive.
Even if we look at farnell for a qty of 50..
https://uk.farnell.com/micron/mt53e512m32d1zw-046-wt-b/dram-...
50 - £9.29 EX VAT
https://uk.farnell.com/micron/mt53e1g32d2fw-046-wt-a/dram-1g...
50 - £12.04 EX VAT
Those are public prices (not even account price) for buying only 50, and there's ~$3 difference even there.