For you to be adopted, you have to be "free and clear" for adoption, meaning your parents either need to willingly sign TPR (termination of parental rights) or the state would need to remove them, involuntarily. This requires both of your parents rights to be terminated, not just mom's.
Due to legalities at 17, it may be easier just to wait until you are 18 and can consent to your own adoption. Yes, you can be adopted as an adult.
I adopted from foster care myself (twice). The only fees I paid was to have a new birth certificate issued, which was about $200 (each).
My parents adopted my mom's sister when she turned 18 years old, because they wanted it to be her idea & decision. She was an orphan at 12, her dad (my mom's step dad) died when she was 5 and my grandma died when she was 12. After my grandma died, my parents finished raising her.. but she was with us most of the time anyway before that. By that age she understood adoption and what it would change for her. So on any given day I might refer to her as either my aunt or sister since she's essentially both.