2000 Dodge Caravan oil leak

I have a 2000 dodge caravan that I took to walmart to have the oil changed. They wouldn't do it because of an oil leak. They took a picture of the oil pan to show me and it was covered in oil. I took it to a mechanic who took a look at just the top of the engine and said it would be $60 for the valve gaskets, $180 for replacing the both banks. He did not look at the underside at the oil pan. I would like to know if this sounds resonable. I appreciate any feed back. Thank you, Susan