Please do read the post again. Cost was never mentioned as an issue, just that they wanted the best solution for the system's purpose, and I did say to use RAID 1 in addition to RAID 0. Not just simply RAID 0 - that is as you said, essential to use some kind of data storage other than RAID 0 for safety's sake.
External backups are nice and dandy, but they are not the super golden bullet many people set out to make them as. External drives are more prone to more shock due to mishandling and I'm just not comfortable suggesting them when in most cases you can buy a couple of internal drives and put them into RAID 1 with redundancy for the actual media archival/storage. Then
maybe an external if you're super paranoid, but I'd suggest dual layer bluray before I ever suggest an external hard drive as a backup solution. Just not reliable enough for long term storage or backups in every case I've encountered. They tend to be more expensive than internal drives, even with the pricing boom going on due to the flooding which occurred in Thailand.
and honestly, if you're buying enough hard drives to do RAID 0 and RAID 1, you may as well just use them all in RAID 10 if the board supports it, and get the best of both worlds. But that's up to the end user and how much effort they want to put into it.