A Rift prepaid game card is an excellent alternative to setting up a credit card payment account to play the game. Buying one of these also provides a healthy discount off the regular monthly cost of playing the game. Rift normally costs $14.99 a month to play, but you can get a 2 month (60 day) prepaid card for $23.99 from Amazon. This works out at $11.99 a month, so you save a few bucks per month. Also, you don't need to risk putting your credit card details into the Rift system- deal with the world's largest online retailer instead.
One of these cards is also a great option if you want to trial the game, but are not sure whether you want to play it intensively. A single month is not long enough to get to know the nuances of the game, but two months will give you ample time!