I wouldn't say that regular desktop DDR3 sticks are "much more expensive". Unbuffered ECC sticks are indeed quite a bit more expensive than registered ECC sticks, but normal desktop unbuffered non-ECC modules aren't....which are much more expensive than ddr3 registered ECC memory that we are all familiar with.
It's just simple supply and demand thing. There's a lot of registered memory on the market since most servers have lots of slots and need a lot of ram (for virtualization etc). Yet the vast majority of simple computers out there don't work with registered modules so when the servers get upgraded there's an abundance of registered modules on the used market and not that many buyers to drive the prices up.
It's a bit different with unbuffered non-ECC desktop modules - that market is pretty balanced since it's mostly people upgrading regular desktops and the number of buyers for those modules is not that huge (average desktop users don't need a lot of ram and usually upgrade their systems to get performance boost, which means getting new platform with ddr4 most of the time).
And unbuffered ECC market is different still - that's where the demand is still strong and the supply isn't. There are still reasons to run servers/workstations that only support unbuffered ecc modules. A lot of those are mATX/mITX low power systems for router appliances, NAS etc - whenever small footprint and low power consumption are important, those still make sense: the boards are cheap, the cpus are cheap (sandy/ivy and even haswell xeons are quite affordable), and the ram is still cheaper than ddr4 unbuffered ecc. But - the supply for those ddr3 ecc unbuff modules is not huge, so they're quite expensive indeed. And if that Dell workstation from the first post would come with 4*8 of those ecc unbuffered modules - then it would be a decent deal indeed. But it doesn't, so it isn't.
I think you're confused about memory types. Dell R220 supports ECC memory (what server doesn't?!), it just needs unbuffered ECC memory. Which is expensive indeed. But that Precision T1650 workstation from the first post has unbuffered non-ecc modules inside (that's the regular desktop memory, which isn't expensive these days).I have a Dell R220 which requires non ECC memory.