Advice for Building/Buying a Mac Compatible external RAID solution

Ok, so I want a RAID array that is compatible with Apple Mac OSX (and windows PC, preferrably, so I could later reformat the drives to NTFS if I so desired). I will be using it for video editing. I am planning to setup 4x1.5tb HDDs in a RAID-10 array (so I'll have 3gb storage with 100% redundancy). Does this sound right so far?

My question is, do I need to buy an external setup such as this 3ware (for $850):

http://www.newegg.com/Product/Produc...82E16822702001

Plus my 4x1.5tb Seagate HDDs such as these ($190 each):

http://www.newegg.com/Product/Produc...82E16822148337

Bringing my total to around $1600?

Or can I build this for cheaper, by getting an external enclosure such as:

http://www.newegg.com/Product/Produc...82E16817332021

or even better:

http://www.cwol.com/serial-ata/5-bay...-enclosure.htm

Plus an $80 internal controller card: http://www.cwol.com/serial-ata/esata...-port-raid.htm

(would this be Mac Compatible and have everything I need? Why does the other one cost $500-$650 more?). I am also wondering if RAID-10 is the best way to go for speed & redundancy, and why some of these enclosures have 5 hdd spots? Why 5?