western digital blue and green which one is better for gaming?

is it right time to get hdd? when price will drop?

RAID is the only "reliable" solution, means you must have at least 2 HDD that mirror each other, otherwise there's no HDD that can last for an interval of time, you won't know how long till the parts start breaking apart, same goes to the very high-end enterprise HDD, it's just enterprise HDD has low failure rate (low, pre-mature failure still exist).
It's either you put on cloud for non-sensitive but can't afford to lose or cut your meals to buy at least 2-bay RAID capable NAS, with the hard disk of course.

Just don't accidentally knock or tip over the casing that housed the HDDs. RAID with only two HDDs only protects you from hardware failure in one HDD. If both HDDs are damaged at the same time...