Yes, the cost progression of storage is expressed by Kryder's law, and is actually faster than moore's law. (well, in terms of storage space, not storage speed.)
Of course, both are observations and not true laws; things will get interesting if/when the capital and power required per unit compute (or per unit ram or storage) stops dropping.
But, my point is that in the past, the costs involved in providing compute infrastructure has fallen dramatically over time, and most people expect this to continue, at least for a while.
In theory, not necessarily in practice. The Thai floods caused a multi-year pause in Kryder's law we're still recovering from. (I'm not sure how robust Kryder's law is - there's a lot less data and analysis of it than Moore's, since that's the famous one.)