Like I said, I've never used on of those sites before so I don't know which ones are good or bad. Maybe someone else knows. I did Google to get a free site.
I am almost positive $100 a month would be more than enough to get started. I also suspect if you call Ameritrade they will talk you thru what you need.
I do my online banking with USAA (anyone can join the banking part) and it's awesome. They created my self-directed IRA brokerage account, and the first 50 transactions are free.
I would find out what your PERS is invested in. If you find out, folks here can "interpret it".
By the way..... I'm 60. You ARE young !!