Gene is correct. You never want to get an appraisal on a home until you're locked in on it. However, if you are going through a lender, you'll be paying for a home appraisal anyway. On the other hand an appraisal goes beyond just knowing if you're getting a good deal or not. You will be paying taxes on your property soon and the value will of a home will determine how much you pay.
But aside from an appraisal, I hope you find a home in a good environment. Enjoy your weekend.