Check out the thread "new here..." by useruser. I give a pretty detailed answer to just about the same question.
As far as cost, it is roughly $4 for each packet at my center.
Also, if you check out the sticky thread for "Alternatives" you will see that there are a lot of people who do IP without going to a clinic and what products they use.
That being said, I like the accountability of IP and going to a center to get weighed in every week. For me, it is worth the money. Also, I know by using IP products I am getting the very best protein and the very best packets. I do not know what is in the alternative products and if it is as good as IP.
Based on your current weight, if you are a "good loser" you can probably expect a 3# average. If you are a "slow loser" (like me!) I would say you will be closer to 2# average. You can see in my signature what my actual losses are, but I am just over 2# average. But that doesn't get me down because I have never been on a diet that had me losing like this. Weight Watchers and Jenny Craig had me averaging 2# a month. I kept a spread sheet when I was doing JC and it took me 28 weeks to accomplish what I did on IP in 7. Best decision I ever made!
Started maintenance on 12/01/11
Time for a reboot. 10/13/15, this time with alternatives