I visited a doctor and he wanted to do 3500 grafts to fix this problem. I am 55 and female.

Doing a hair transplant to treat diffuse thinning in a female of your age is malpractice in my opinion. The single best treatment for you is the appearance of fullness which can easily be accomplished with Scalp Micropigmentation (see: https://scalpmicropigmentation.com/smp-for-women with many examples of women like you)