Just be careful about starting Restasis if you aren't sure that you can afford to purchase it regularly. I hear that once your eyes get adjusted to it, going off of it can be a rather difficult process. In fact, my eye doc simply said, "Once you start it, you need to be on it forever."
Stopping Restasis creates a rebound effect that leaves your eyes VERY dry and uncomfortable. I have a friend who was on it for allergies and stopped after a while. She said that going off of it was terrible. You may be better off sticking with non-prescription eye drops if you have concerns about keeping up with Restasis.
I do agree with everyone that one box can easily last a month (or even a little more--my insurance for my new job doesn't kick in until next month, and I intend to really make the box I have stretch).
Also, not to continue being a down-er, but you should also know that Restasis doesn't work for everyone. It helps some people a lot, some a little, and some not at all. I receive some relief from it, but not much.