Hi Michele, I use a firm called Travelex to buy euros on-line. Usually get a good rate and no commission. Order and pick up a your departure airport. I think most airport sites which have an on-line currency order facility will have a link to Travelex.
One thing though, if you buy from them at the airport desk you will pay commission. Also take into consideration any charges your bank might make for using a debit/credit card to purchase on-line. Buying currency is treated by many banks as a cash advance transaction.
We have a Nationwide Flex account which means we can use our debit card without incurring any charges. Also works in the hole-in-the-wall machines without charges.