First off, why take all that money with you? You can pay for most things with a credit card. Bring some cash, of course for smaller items, but ATMs are ubiquitous, so no need to bring a huge was of US$. Check with your CC company and bank first, though, to see what FEX fees they charge.
I agree with the others that it's hard to recommend a budget amount without knowing your preferences and spending habits. Using the cost of the DDP for food, assuming you'll only eat within those parameters, works for some. Otherwise you'll have to look at prices on the Disney menus and add them up yourself. It's not just the alcohol that can damage a food budget. Those Starbucks lattes, Dole Whips, or Mickey bars aren't that inexpensive either. Speaking of snacks, many resort guests will order a grocery delivery or make an Uber run to a nearby grocery store for snack items as well as water (the tap water iastes terrible, as you know), soda, beer and wine. Also consider getting simple breakfast items. Eating breakfast in your room while getting ready for the day on some mornings saves money and time.
Souvenirs - can quickly ruin any budget if you're the impulsive type. We've been there so often, and thankfully are no longer bringing little children who want everything they see, so our budget in that department has shrunk considerably now.(and is somewhat proportional to the decrease in quality of most of the usual trinkets). Bear in mind the weight and volume of all your purchases. You won't want to pay for an extra checked bag on the trip home. Mind you, a 500GBP Mickey Mouse watch weighs little, and doesn't take up much room.
A PP mentioned other costs. Taxis or Uber costs can add up over time if you use them a lot. Taxifarefinder is a useful site for cost estimates.
