It depends on the plan you choose. There is the 10 dollar a month subscription fee. Then there is the choice that I recommend, not only because I use it as well, but because it makes the most sense. The 60 dollar a year plan will cut your yearly price in half.
There are two different types of membership for XBox Live. One is the silver membership which is free but your access is limited. XBox Live Gold memberships are $7.99 a month and offer access to everything XBox Live has to offer.