Board game is fun because there are a number of aspects in which players may influence the outcome of the game. Managing these different levels of play at the same time is quite a challenge.
The card game is a CCG, a Collectible Card Game. The biggest and most successful CCG is Magic: The Gathering. I do not like Magic at all, it's just a generic fantasy concept constantly changing with new card sets. But I've thouroughly enjoyed the AGOT CCG.
One reason for my enjoyment is that GRRM has created a fairly complex and realistic world that is the basis for the CCG. I don't have to have an excuse to battle an opponent because the great Houses of Westeros are constantly battling for rank and power. I don't have to hear my opponent say, "I'm Schnickelfritz the Wonder Mage from Flugdorf! I send my blind lab mice of Doom through the Jello Teleporter to destroy your mint julep processing plant." I like my fantasy a little more realistic than that.
The second reason I like the card game is that I must compete on three different levels in the same game. Each player can make and must defend against Intruige attacks (obviously the Lannisters are great at this), Crown attacks (this reflects court influence and the Baratheons are good at this), and Military attacks (the Starks are good at this). To influence these battles each player has location cards (for instance possessing The Iron Throne will give a player dominance at court), attachment cards (a Valyrian Steel Blade can turn even Sansa into a killer), event cards (slipping Tears of Lys into the Mountain's drink will ensure he'll kill no more of your men), plot cards (sending your opponent's knights to serve on the Wall is fun), and the all important character cards (the Blackfish is a monster).
The other reason I like this CCG is that you can play with many players at the same time. I've played with five players before, and I'll tell you that even the best players cannot singlehandedly take on three opponents at the same time. Diplomacy is key.
The bad part about this game is that it's a CCG. I think the board game may be purchased for around $50. For your money, you'll get all you need to play. A CCG on the other hand survives on expansions to the original set. There must be at least six sets for AGOT. Anyway, you can buy one pack of cards for $3.25. Each pack contains 11 cards. Each pack has different cards and each set is made up of 200 or so unique cards. So I'd guess there are over a thousand individual, unique cards for AGOT. If you purchased these thousand cards by the pack and never got any duplicates, you'd spend over three hundred dollars. But you will get duplicates because the cards are printed as commons, rares, and uniques... and uniques are the best cards.
Of course you do not need all the cards to play. I think most fans of AGOT will find that they are drawn to one or two of the major Houses and that they tend to despise one of two of the Houses. So if your husband likes the Starks and hates the Lannisters, then he'll not really need to collect Lannister cards... but when you purchase packs, you cannot select your cards... you have to take what you get.
The playable Houses are Baratheon, Greyjoy, Lannister, Martell, Stark, and Targaryen. You can also make Tyrell (from the Baratheon and Lannister decks), Tully (from the Stark deck), Wildling, Clansmen, Night's Watch and general unaffiliated factions from the unaligned cards.
Anyway, there is more to the game than this. I've not collected any cards, nor even checked up on the game in the last two years. My information may be out of date, sorry. You can find the official CCG website here.
A Game of Thrones CCG Tournament Site
Your best bet may be to find people selling their cards on Ebay or Craig's List.
