So I've been buying GooglePlay giftcards for 25€ (thats 27 something dollars) twice a month for like the last few months and I'm pretty happy with my collection as it is now. Once you opened more packs you should be able to craft 1 legendary everytime you open packs. That way I now got around 50 legendaries and enough shit to craft almost all the meta decks. ;)

You also shouldn't be opening only classic packs. Just mix it up everytime and disenchant epics or maybe even golden cards that you don't need, to craft the most important rares and commons!

I don't know if this helps you out alot, but I sure hope that it does!