I had an ElastiCache redis running on Amazon and forgot to turn it off after testing for a month. And today, they charged me USD230.
Since this is my first time using Amazon and not even using a lot of memory, I'm just wondering if it's that expensive. If it is, imagine running full 16GB redis.
They certainly can be that expensive; for an ondemand instance pricing could be as low as around $12/month for a micro instance with ondemand pricing and as much as about $2750/month for a single r3.8xlarge.
Bummer that you wasted the money, but it could have been a lot worse if you had spun up their biggest instance to test on.
I often worry about making mistakes like that, so I review my costs almost daily, but at least every few days.