Call a few CPAs, describe what they would be auditing, and ask about cost.
Though some would value a big name as auditor, the process would be the same for all. Therefore, any qualified audit should be as good as another.
Prior to being registered with the revenooers, your past performance is not required to have been audited. However, your statements of returns must be "auditable"... that is, if they *were* audited the results would conform to regulations. After registration and dealing with the public's money, you'll likely be required to have an annual audit. (There are exceptions to the audit requirement, however... one exception is where you do not have custody of customer funds.)
