De Groot et al.  analysed 94 restoration projects globally and found costs varied by several orders of magnitude, but in terrestrial and freshwater ecosystems mostly in the range of USD 100-10,000 per hectare. They did, however, estimate that the majority of these projects provided net benefits and should be considered as high-yield investments. Some methods can be much cheaper than others, even in the same type of ecosystems in the same country; the estimated cost of restoring forest cover in Brazil varied between a mean of USD 49 using natural regeneration compared to a mean of USD 2041 per hectare
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report