>>58061206I started with the Miraidon deck but most cards in it aren't legal now. From what the anons here have told me the Charizard League Battle deck is good but apparently it's a bit more expensive right now. Probably because it comes with a really good staple that a lot of decks use (Fezandipiti EX). In my opinion you should look up the current playable decks and just buy singles to build it. Some of them can be pretty cheap believe it or not. I built Festival Lead (a Dipplin grass deck) for about $30. It's pretty fun and can take down some of the strongest decks occasionally if you can get set up.
You could also do what I did and try to make your first deck around one of your favorite Pokémon. My first deck was Alakazam EX. It's not exactly meta but it is fun. Using a Pokémon I really liked pushed me to learn the game.
But I'm still somewhat new too so maybe this is bad advice 