Help my kid wants Pokémon

I was there from the beginning when Pokémon arrived at card shops. It was cool for like a year when I was in 3rd grade, then my friends and I moved on to new hobbies. I will never forget the thrill of pulling holos. 25 years go by, my mom threw out my card binder, and now I have a 6 year old who found Indigo league on Netflix and wants to start collecting the cards. Where do I even start? The hobby seems to gave been ruined by adults, scalpers, grading, and investors. On top of that, there are now 1,025 Pokémon????

Two goals:

1. I would like to get two simple playable decks to learn gameplay together.

2. If she’s wants to start a bigger collection, where can I get cheap “used” cards? I don’t want to take away the excitement of opening a fresh deck, but I have a hard time believing this hobby is going to evolve into a serious long term investment and will probably eventually fizzle.

Thanks.