Most churches conduct a financial review each year. If you think the financial processes and systems are well tuned, a review should be adequate. Guidelines for a review are available at crcna.org, search for finance and administration, then find the section "Audit" under "Financial Management".
If your church believes you need a financial audit, the least expensive way to start is by contacting a CPA that attends your church and connecting with them for completing an independent audit or a referral to a local CPA who could complete the audit.
The deacons at our church our looking into having our financial records audited. Is there anyone in west Michigan who has had recent experience with this. Are there any Denominational agencies that work specificaly with churches.