Not sure about the quad safari but the jeep safaris are brilliant! If prices are same as last year (and they were in early January this year), a large beer (Efes) averages around 4-5 lira although you will see offers around the town. Spirits aren't cheap as they're imported - you should see the prices of a bottle of Malibu for the bar owners!! Food can be as cheap or as dear as you want really - the kebaps are great after a night out and there's loads of small cafes where the prices are reasonable, right up to some fantastic restaurants where you can spend as much as you want.
Trips are usually good value - don't buy them off a rep, there's loads of agencies in the resort and you can often work some deals when booking more than one. Don't miss the boat trip - great value for money and a great day out.
Depends what you want to do really - Kedi says your hotel is 18-30 so I'm guessing you'll be on Bar Street a lot? Now this is only my opinion (and I may get into trouble for this) but I don't find the drinks as strong on Bar St (and certainly not the free shots they entice you in with) - or maybe that's just me getting older LOL!!
As you're in apartments, you will be able to buy food in to have a snack. There's a good small market in Gumbet on a Sunday and the fruit, veg, cheese, etc are dead cheap - and there's a bread shop opposite so you can always make a butty! If you want to have beer, pop, etc in your apartment, it may be worth a trip to one of the supermarkets (there's Kipa, Migros, etc on the main peninsula road) - there's a couple of cheap ones (think Lidl or Aldi) on Ismet Inonu Caddesi (the road from the windmill to Gumbet junction - you'll soon find where that is) - I can't remember their names but maybe Kedi knows.
Any more questions, just give us a shout - we have a house in Gumbet and visit about 5 times a year.