Is there a money changer in Disneyland Paris?
If you are in the UK the best rate is at the Post Office and they charge no commission. At Disneyland it is a captive audience and the exchange rate is not in your favour. If you have a debit card from Nationwide B.S. you can get French money from distributors in France without a commission being taken either. Bear in mind that when you come back to the UK you can only exchange back notes, not coins, by the way.