Microsoft's UFS storage surcharges, German prices in € incl. VAT:
+_64GB +€120
+192GB +€240
For comparison, Samsung M.2 SSDs in the retail market:
_64GB outdated
128GB outdated
256GB €_23
512GB €_34
__1TB €_40
__2TB €_95
__4TB €282
Some other manufacturers offer cheaper SSDs.
Microsoft tries to pull the total rip-off. UFS is worse technology than SSD. The prices per GB are exaggerated by up to the factor 50. Apple can do it so Microsoft thinks it can also do it. There is a reason why Microsoft does not enable replaceable storage while every other component becomes replaceable. It wants to treat the potential customers as idiots.
Never buy upsold hardware!