SSD still costs US$2-US$4 per gigabyte. Spinning rust costs US$0.10-US$0.20 per gigabyte. SSDs are much faster but disks are still twenty times bigger at the same price. A developer hour costs on the order of US$100. If your service uses more than a few gigabytes per developer hour, it's worth some development time to optimize for rotating disks. Whether it's worth increased time to market is harder to calculate.