We are using Hush Hush Little Baby when our daughter arrives at some point in the next few weeks:
http://hushhushlittlebaby.com
The rates are generally $25 to $30 per hour, and most night nurses stay for 8 to 10 hours - so that's anywhere from $200 to $300 per night depending on hours and level of experience. The selection process was easy: we told a manager our expected due date, and she sent us background information and experience information on a few potential nurses who would be available around the time of our due date. We held a phone interview with one and agreed to work with her. The plan is for her to come to our house for about 10 nights over the first few weeks (perhaps every other night or every third night depending on our needs). Our parents are elderly and we thought it would benefit us to have another set of hands around the house -- especially to help with late nights feedings, diaper changes and burping -- as we get more comfortable with the "new" routine.
The cost is expensive, but I think the extra help will be worth it. Other friends have opted for night nurses or full-time nurses, and they have had very positive things to say.
Good luck!