The economics of climate change are complicated. Yes, it costs money to implement solutions on a large scale. It's important to think of these solutions as investments. Project Drawdown has compiled the top 100 solutions to combat climate change, and almost all of their solutions pay for themselves many times over by 2050. Explore some of these exciting (and profitable) ideas here.
There is also a cost to going about business as usual, often called the "social cost of carbon." Think about the damage that record hurricanes, wildfires, floods, and droughts cause. Carbon dioxide emissions are economically categorized as "externalities," meaning they have costs but are not captured in the market price of goods. For example, a fossil fuel company produces energy for $0.10/kW and sells it for $0.11/kW, but it does not include the negative impacts of the carbon it emits in its accounting. Instead, those costs are eventually paid by those who suffer the impacts of a warming world. Currently, the U.S. EPA uses a social cost of carbon dioxide of approximately $42/metric ton. Learn more from Nobel Prize winning economist Dr. William D. Nordhaus here.
Climate change is also an ethical and global issue; it can't be reduced to a simple cost-benefit analysis. For example, Dr. Nordhaus estimates the economically optimal solution to be one that allows a warming of 4 ° C. However, this solution does not take into account the irreversible events the Earth would pass on its way to 4 ° C. Island nations would likely not survive the unrelenting hurricane seasons, despite contributing very little to global emissions. It is not an ethical proposition to justify the loss of a country and people because it is economically "optimal."