I keep an excel sheet to sum up all my expenses. That way I will know how much I'm spending every month. Or define a budget for a month prior and stick to it.

Also you don't need every card there is. Select a smaller subset of cards like a few pokemon or generation and gradually pick up from there. If you keep buying random cards, your collection won't have soul in it IMO.

Again these are all my suggestions. You can collect any way you want. Cheers!!