Looking for a way to do a VLookup in one array, if value not there go to a second array

I have a part number list showing part number, description and a selling price amount in USD. I use this to to look up the description and amount where a series of PNs are entered elsewhere in the file, then I further manipulate with quantities and sum the result. I also have an option for other currencies showing a currency name and exchange rate. I use the exchange rate to manipulate the USD amount. Now the problem. We have some exceptions where we have predetermined a fixed amount as the price of some of the parts in the foreign currency. So I built a second table with the exceptions. So what I would like to do is be able to do a VLookup in the exception table and if the part number is not found do a second VLookup in the the main table. If I find the part in the exception table, I will use the amount as is. If I don't, I will find the part in the main table and then multiply by the exchange rate.

Thanks. Also, I just uploaded a file as suggested.

Thank you. It works!