As long as you are able to keep up with the laundry demand (assuming you buy your own dipes, which I recommend), CDing is ESPECIALLY cost effective for twins. Both from the $$ shell out for disposable diapers, and saving space in your garbage can.
What I would recommend is to get a diaper service (if available) for the first month, especially if you've never CDed before. That will help you figure out how much you need.
You can also order a 'sample pack' from many CD sellers with different styles of diapers and wraps, that way you can experiment for fit and ease, and after a month or two you should know A) whether you want to purchase your own and B) what kind you want to buy.
Some folks buy a lot of dipes up front, but what can I say, I'm a pennypincher...and didn't want to spend all that without even knowing what system would work best for my kid. My boys wore their sisters' handmedowns, and I knew what kinds of stuff I liked best so I just got more of it.
I think CDing twins is totally doable.