Ok...
Transport
Use the bus wherever possible, its only about 2 Euros a trip and they run pretty much everywhere.
Taxi's if you have to use a taxi try getting vocal in the que there maybe someone else going to the same place as you and you can split the bill
Some clubs such as El Divino will refund your taxi fare if 3 or more of you share a cab to the event, you need to get a reciept and claim it back at the club.
San Antonio has some bikes you can hire , there is a thread about them on here somewhere, i think you just leave a deposit and you get it back when you return them.
Drink
last year we bought a bottle of Smirnoff Vodka and a pack of 4 redbull for 14E , that night i went into manumission (Privilidge) and bought one Vodka redbull for 14E! so that gives you an example of what you are up against.
Plenty of cheap drinks to be had in the local mini market have a couple before you go out to get you in the mood, you can take this to extreames ie: Carton of red wine 1Euro!
the Westend in San Antonio will give you best value for money when out for a few drinks and unlike the TV programmes of years gone by is not a bad place to be, its very vibrant and lively.
Drinks in the big clubs are ALL expensive, full stop water is your best option here ask for a glass with ice if you can it will make it last longer, failing that a bottle of San Miguel is the next cheapest if you want alcohol.
Food
Again lots of cheap options from the minimarkets, but there are lots of places to eat all over the island some cheaper than others, and cheap doesnt have to mean KFC or the like there are plenty of places offering healthier alternatives at a reasonable cost.
Money
try and work out a rough budget for each day and stick to it , maybe have an "emergency fund" (I normally have something like 20 or 30 E folded over in the back of my wallet) just incase , it will get you cab home if you get stuck.
Not all the good things in Ibiza cost money:
Watching the Sunset
The Beach
Lounging by the pool
meeting new people and chatting
have a walk round your resort town , explore you never know what you might find
Take plenty of pictures, you will always wish you had more to remind yourself of your trip.
Club Tickets
Either here (Spotlight) of Clubtix (online) will be your best bet , or buy them from places like Mambo or any of the bars selling them in San An , sometimes they do free transport to the club thrown in , shop around and make sure they are genuine tickets.