They certainly won't cost millions if they are proactively managed. And any costs need to be factored against the considerable value of the ecosystem services they provide such as buffering against flooding, droughts and wildfires, enhancing biodiversity and with that ecological resilience, recharging aquifers, carbon sequestration, filtering agricultural fertilisers entering waterways, etc.

https://onlinelibrary.wiley.com/doi/abs/10.1111/mam.12220