Garbodor is one of the most format defining cards there is right now and it's just a few bucks for a playset. Last format, Vespiquen was one of the biggest decks, and there have been lots of good non-EX/GX decks in the recent past. Expanded has a lot more non-EX/GX focused decks right now.
Most decks will use both GX and non-GX pokemon, if you run a non-GX card you can force your opponent to take 4 KOs instead of 3 against a pure GX/EX list.
And in terms of expenses, Tapu Lele-GX is the big cost barrier, everything else is pretty cheap. Gardy/Golisopod are like $10ea but the average GX card is $3-6. Lele is like Shaymin-EX last format, it's expensive but you use it in every deck, so once you've got it building new decks is cheap.
Most decks will use both GX and non-GX pokemon, if you run a non-GX card you can force your opponent to take 4 KOs instead of 3 against a pure GX/EX list.
And in terms of expenses, Tapu Lele-GX is the big cost barrier, everything else is pretty cheap. Gardy/Golisopod are like $10ea but the average GX card is $3-6. Lele is like Shaymin-EX last format, it's expensive but you use it in every deck, so once you've got it building new decks is cheap.