Depends where you go, you get a half decent meal in the evening for 20 Euro each including a drink, you can pay less if you just want some chips and a burger, or more if you want something special.
Clubs and the bars associated with them are the killer, a bottle of San Miguel will cost you 10 Euro in Space, Pacha or Amnesia and Spirit's are even more. So say you both have just four bottles each, just at the club, that's 80 Euro gone already! It can be expensive getting in too, Pacha is 70 Euro if you turn up outside but you can get offer's on tickets which I imagine 99% of people go for. You can get a ticket and bus from Mambo to Pacha for about half the price I think. Mambo, Cafe Del Mar and Savannah are expensive too, not ridiculous like the clubs but not cheap either. If you go over the sand dunes from mambo towards the coastline apartments there's a place called Kanya which hosts quite a few pre parties, it's just been re-furbbed and while it may not quite have the Mambo atmosphere, it's done really nicely and it's quite cheap for drinks compared the others, definately worht checking out.
Me and My Girlfriend went for a week and took £1000 which gave us about 1400 Euro. We were spending about 20 Euro a day on Cabs, a meal in the evening, drinks pretty much when we wanted, a few evenings at Mambo and we did Pacha, Space, and Amnesia. It was probably just about enough to not have to worry about what you were spending, If your going clubbing then I wouldn't want to take much less than that for two people for a week though.