ECC UDIMMs have always been more expensive than their ECC RDIMM counterparts, but I don't think it is because of manufacturing costs (as the RDIMMs have even more ICs on them than ECC UDIMMs), but more or less a supply and demand issue since in the used market ECC RDIMMs are everywhere vs ECC UDIMMs which are even more niche than just UDIMMs--even the DDR3 variety, where prices for 8GB ECC UDIMMs still cost far more than 16GB ECC RDIMMs.