There are 60-day game time cards available for NA now.

You do get a discount for 90 or 180 day subscriptions. It's $1 off per month for 90 days, $2 off per day for 180 days (and the same if you pay with Crysta). Those are only available as recurring payments, but you can do so with either Crysta or a credit card. Really, the only difference between using Crysta and using a credit card is that you're using Crysta instead of a credit card.

You won't get these discounts with game time cards, since they add a flat 60 days to your remaining time and they're at a fixed price.