Geoengineering is not yet affordable. Just as any new technology, it takes a lot of money to make it profitable and able to be mass marketed. However, just because it is not affordable now, does not mean that we should abandon the idea. Given time, it will be cheaper and easier to complete.
Geoengineering is an untested science, and it will clearly cost more than it is worth. Every new form of technology is overly expensive and dangerous when it is first being developed. Geoengineering is no different, and no company or government has been able to show that it will be affordable in the future.