I have been a long time collector of the Pokémon card game. Love the game and what the cards did for me as a kid. If your looking to get into collecting or have been collecting for a while, I'm here to help maybe save you some money, for the cards you want.
The single packs are the most expensive way to buy cards. Yes you can get really rare cards from them and they are the cheapest from buying to boxes. That is a hard way to gain a collection though.
From these you never know what your going to get an a high chance you'll end up with the same cards multipole times. So in the long run you will waist a lot of money.
Now the starter decks are great way to get the ball rolling. Granted you can still end up with a ton of copy cards, but you know what your getting for the main rare card. So this way I find best to start a new gen or to start fresh. Word of warning the EX boxes are not worth it unless your in it for all it comes with. So just the basic playing cards not worth the box. Everything Pokémon that you can get your hands on. I would say good buy.
The internet is my favorite and cheapest way to get a collection you want. Amazon and eBay really help in big ways. I like amazon more then eBay. But that's just because I want it fast and I don't need to deal with anyone else. On eBay you can find a lot of cards for a good price. However the seller could rip you off aka fakes or give you poor quality of cards. You really need to know what your looking at and read there reviews to know. Now amazon you just look up the card you want an buy. Simple and easy. 90% or the time its a good price so look around if your not sure. The link that I have below will take you to the cards right away on amazon. You can copy and paste if you cant click on it.
<a target="_blank" href="https://www.amazon.com/gp/product/B000WD3XBI/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=B000WD3XBI&linkCode=as2&tag=publisher0d-20&linkId=63063a3e61534f3daa8b9a0ebe673ff8">100 Assorted Pokemon Trading Cards with Bonus 6 Free Holo Foils</a><img src="//ir-na.amazon-adsystem.com/e/ir?t=publisher0d-20&l=am2&o=1&a=B000WD3XBI" width="1" height="1" border="0" alt="" style="border:none !important; margin:0px !important;" />