The IRS has stated that beginning January 2008, the standard mileage rate used for personal cars - which also include mini vans, pickup trucks, SUVs, and panel trucks - will be as follows:
-14.0 cents per mile driven in the service of charitable organizations.
-19.0 cents per mile driven for medical reasons or moving purposes.
-50.5 cents per mile driven for personal cars driven for business purposes.
From the information that you have provided me, you receive a reimbursement payment from the Churches (which I am assuming therefore, that you will receive a 1099-Misc at end of the tax year), and so would be allowed to deduct 50.5 cents per mile as the work performed by you appears to be a requirement by your employer for which you are not being reimbursed.
In terms of the record keeping, clearly one would like to keep official receipts but for mileage records, you won’t have a receipt! Therefore, it is recommended that you should list your odometer readings to claim mileage. It is suggested that you should mark your vehicle’s odometer daily business mileage in a diary or a daily planner.
In this manner, at least you will be able to substantiate to the IRS in an event of an audit, that you incurred some business mileage and had the auto mileage log to support your mileage position.