You can buy cheaper tickets from Last Minute Travel Club than anywhere I’ve seen (you have to join, they say it’s $50 a year just google a code and your free forever).
Food wise: look online for their menus to get an idea but for 1 person, quick service (or fast food outside of the resort) go for $30 a day for some buffer room. Maybe another $5 for a snack everyday.
Water: buy water from target, CVS,
amazon prime etc. it’s $4-$6 in the park and at most of the nearby hotels. You can bring water in with you everyday, they also have water refill stations in DL at the restaurant near Buzz Lightyear. You can also sometimes ask for free or very cheap water from most quick services counters.
Spending: depends on what you want to buy. Ears -$25ish, shirts- $40, hats - $30?, hoodies-$50-$80, pins $15
Getting around: you can use Lyft/Uber or public transportation like the ART. You can get a Uber/lyft estimate online from place to place. FYI if you do use rideshare maybe see if they have any specials. Last week we realized if we ordered from ubereats for dinner we could get 50% (up to $10) for 10 Uber rides. Made our quick trips to DL or the store $3-$5 each way. They sometimes have 10% off during the week for Lyft. Or other coupons for so many trips for cheaper.
Universal Studios: food/spending is about the same price as DL. You can also buy a refillable cup and refill it all day at most of their food places (it’s a rfid chip and you just use the soda machines or can get tea/water).
Hotels: that depends on what you want, expect, and price. You can get one for super cheap though