It's not so much that the AI is cheap as much as their decks are at least decent and the default deck is completely irredeemable. As hard as it is to get cards it might be worth it to buy the DLC, but as far as I know everything in the DLC can be obtained in-game with time instead of money.
If you're just starting out and have plenty of points to spaore, I say go for all of them. The deck you start out with is garbage and everybody else has decks that greatly overpower yours. Plus they can give you some ideas on what you want to run for online.
Just remember, once you get enough cards to make an Empty Jar, Necromill, or especially a Chain Burn deck for quick grinding, make one immediately as those will get you the most cards.
SF4: Dictator | TTT2: Feng/Dragunov | SC5: Cervantes A sound soul dwells within a sound mind and a sound body.