Is $12,500 to improve attic airflow, remove old insulation, treat for growth, and install new insulation a fair price?

I bought my house back in 2019 and no issues were noted on the inspection. I had a container of books up there and when I went to pull them down I noticed the top of the box was wet. The guy from the company said that I do not have enough airflow in my attic and condensation is occurring. He also stated that my house was built without soffits and that the only thing venting the attic was a gable vent on both sides of the house, and a couple roof vents. I legitimately don’t know much about houses or insulation in general so I’m just looking for a second opinion here.