I was looking at getting the Xeon-based NUC recently and one of the reasons I decided against it was that ECC SO-DIMMs seem to be a really marginal product. If you want ECC, something that takes full-size DIMMs seems much easier to buy memory for.
Note that the price is mostly due to market segmentation, in your case most of it by the laptop vendor (of course some for Intel, but not that much compared to the laptop vendor)
Xeon with ECC are not that overpriced compared with similar Core without. Likewise, RAM sticks with ECC are cheap to produce (basically just one more chip to populate per side per module). Likewise soldered RAM would simply add maybe $10 or $20 of extra chips.
For the price, it made more sense for me to buy an R630 and populate it with a few less expensive, higher capacity ECC RDIMMs. I don't really need ECC as a local feature, so this lets me run on the mobile I want.
Bit flips happen and are real. I really wish ECC was plentiful and not brutally expensive!