What tests are they proposing to administer? I would ask for a list ahead of time and double check that you are getting what you want out of this expensive testing. IQ testing alone will not be definitive re dyslexia. Here's a link that talks about various tests and how they can be used to identify dyslexia. It also has a link to a document about dysgraphia testing.
http://www.concordspedpac.org/Whichtest.htm
A neuropsych eval also may identify other potential causes for your child's issues that present with similar symptoms.