The maintenance on enterprise storage is generally a percentage of purchase price. So it's actually cheaper.
>How much do you pay to keep those HDDs powered per TB per year?
4.5 watts idle/8 watts max for a spinning drive vs. 4.5 watts idle/11 watts max for a large capacity SSD (15TB Samsung). The power consumption thing was a much better story comparing 3.5" 15k RPM drives. 7200 RPM drives it's basically a wash unless you're talking about relatively small capacity SSDs.
>How does the low IOPS of those drives affect your workload?
That's really the crux of the issue. SPINNING drives are not dead. FAST spinning drives are dead. 10k/15k drives are going to see the end of their useful life in the modern datacenter far faster than anyone predicted 2 years ago. Outside of legacy systems I would expect sales of 10k RPM drives to fall off a cliff if not completely disappear before the end of 2020.