On DKK900 you'll have to watch where you go. If you're on the sauce, get a carry out or limit your intake (maybe a bit naive on my part ...but hey you asked
), eat from takeaway pizza type/Burger King places and use the S-tog (city train) to get out there and you might be okay. Walk into a tourist trap pub or eatery and your money will go pretty fast. Also tickets on trains in and out of the airport wont be super expensive but might take up DKK50 each way. Train to Glostrup or Brondy (closest stations but both about 3.5km from stadium) might be a bit more again, so you could be looking at DKK250-300-ish on trains. If you chance it without a ticket and get caught the fine is over £100 and the Danes take that stuff reasonably seriously. As long as you have a back up up credit card or some other source of funds in case you go over limit you should be able to stay close to that...again as long as you watch how you go. Hope that helps.