It's very very rare that decreasing demand increases the cost of something, unless it's been entirely replaced by something else (e.g. horse carriages vs. cars)

It's very very rare that decreasing demand increases the cost of something, unless it's been entirely replaced by something else (e.g. horse carriages vs. cars), which -- when it does happen -- is mostly due to supply side reconfiguration that leads to higher marginal costs. So no, I don't think your causal direction is plausible without strong corroborating evidence.