One "Trick" to getting started is to buy your 500 MGP for 5,000 gil, earn another 20, buy the "Bronze" card pack for 520 MGP clearing out all your MGP, then buy another 500 MGP for 5,000 gil and earn another 20... But that only gets you up to 6 new cards for super cheap. After that, there are two more cheap cards (Chocobo and Moogle), and then you can go for the Silver card pack, which is nearly half off if you use the above trick (getting just enough for one, going down to 0 MGP, then buying your MGP back up to 500).
I kinda wish this wasn't so P2W, but it is, so you might as well use that to your advantage. The way they could have stopped this tactic is to prevent you from being able to buy anything if it would put your MGP below 500. So, you can go below 500 for like, entrance fees and challenge fees and so on, but you can't buy items with that 500 point gil-buyable reserve.
The cards in the 520 MGP Bronze pack are:I'm assuming that you can get unlucky and get a card you already have.
- Behemoth Card ***
- Scarface Bugaal Ja Card **
- Coblyn Card *
- Goobbue Card *
- Pudding Card *
- Spriggan Card *
However, the cards in those packs, and the cards that can be bought individually from the card trader, can be obtained in other ways. I won a Chocobo card from one of the Gold Saucer NPCs while trying to earn enough to buy it, and I've won a Scarface Bugaal Ja card from the same guy. It seems that when you win, there's a random chance of winning a card, but it's not a very high chance. If you already have the card, you can't do anything with it except sell it back in for a few MGP (10 MGP for a 2* card).
Has anyone been able to determine:
1. What cards are in each of the other packs
2. If specific NPCs can only drop specific cards (maybe only the ones in their deck?)
3. If the rank of an NPC (ie: the cost to challenge them) determines the cards they can drop (mutually exclusive with the above)
4. If specific NPCs have unique cards that can only be obtained from playing them and no one else
So far, I've won a Sylph card from... crud, I forget if it was Mother Miounne or Maisenta (I think Maisenta), and a Scarface Bugaal Ja card and Chocobo card from .... the first guy on the right as you enter the card area (forget his name).