We are currently using hourly rates (around 100€/hour (130$/hr)). Rate is quite reasonable for our expertise level in our area. However, I have noticed that it scares smaller customers away.
I honestly don't know which one would be better approach: crude week estimates and price tag of 4000€/week/person, or detailed hourly estimates and 100€/hour/persons. Of course value based rates would be best, but not really possible in most of the iOS projects that we do.