My vote is if you want to play now, buy now. I just started and my tips for being thrifty:
-Buy singles when possible. I bought both Team Up theme decks when Best Buy had them slightly on sale and the price of Cynthia dropped. I realized that the price of singles will always follow the sealed product availability. I think theme decks might = the cost of the cards you need if you can find a great deal, but I wouldn't otherwise (Example: Best Buy had Blazing Volcano for 7 bucks, which is a steal considering you can sell the code card).
-If you obtain PTCGO codes, sell those online (I believe it is allowed to sell codes because they are linked to you having an IRL, physical code card). For example, Theme Deck codes/Booster Pack codes
If you really cannot afford it, try using proxies for now, as I think League casual play tends to allow it.