No, an optometrist told me that the prescription for eyeglasses and contact lenses are different. That because the prescription glasses lenses put in front of your eyes while the contact lenses are put into your eyes. So, you'd better take eye exam again. I think it not worthy to risk your eye health just for save $100. If you really want to take eye exam, you can ask an optometrist if he/she can turn the prescription for contact lenses use.
No. A glasses prescription is not suitable for contact lenses. Because contact lenses are placed directly on the eyeballs while glasses are sitted away from your face. Generally speaking, a glasses prescription is stronger than a contacts prescription. So you'd better have another eye exam to get the prescription for contact lenses. You can go to walmart to have an eye exam which would cost you less. It usually costs about $50 for basic eye exam.
Both answers above are more or less correct. Contact lenses prescriptions include at least 2 additional parameters, base curve and diameter, which are determined by your eye care provider when you have an eye exam and contact lens fitting. Read this article @ http://www.contactlensespedia.com/contact-lenses-types to learn more about contact lens prescriptions.