In raid0 you have two drives, if one drive fails you lose ALL data on both drives. hense 2 vs 1, greater chance one will fail
Not all drives are recommended for Raid0, most lower end drives should not be used in raid.
Newegg currently has the Samsung F3 1 TB drive on sale for $80.
Check out the reviews on newegg for the drive you are thinking of getting, some of the Newer drives get real Low marks on reliability!!
DON't get Hung up on sata II (3) vesa sata III (6) drives. SATA III (6) is simply a marketing tool as they DO NOT have any better sustained throughput.