I pretty much agree with Cheese.
Europa-Park has an enormous amount of rides, attractions and shows - but more than 3 days can, for most people, be a little excessive (although I expect the threshold to go up by 1 day once the Water Park opens in 2016/17). Your plan of 2 1/2 days seems absolutely spot on. You will get on all the rollercoasters in that time, and all of the dark rides, plus the water rides - and some re-rides on your favourites. I'd also make sure you stop by at least the Variety Show and one of the Arena and/or Ice Show - depending on your tastes.
I presume you are in one of the resort hotels?
As for budget, it's really a question of how much you like to eat and drink!
I tend to base my spends on an average of €60 (£48) per day - with some days costing less.
Typically, on park, a lunch at one of the mid-range self-service outlets (i.e. See-Restaurant, Pizzeria Venezia etc.) will set you back around €14 (£11.50) for a main course, dessert and drink. The burger outlets in Russia and Germany, or the more 'light' options such as Bamboo Bay Wok Restaurant in Holland, Kaffi Hus and Moby Dick Hot Dogs in Iceland or the Colonial Restaurant in Adventureland will cost you around €7.50 (£6) with drinks.
Drinks in the park cost from €2.30 (£1.90) for a small up to around €3.20 (£2.50) for a large.
As for evening meals, costs vary a lot depending on where you go.
The cheapest 'proper' restaurant run by Europa-Park is Silver Lake Saloon, which is at the Camp Resort - a 15-20 minute walk from the resort hotels. Food and service is excellent, and there is live music and/or entertainment pretty much every evening. It's a steak house mainly, with burgers, steaks and salads. Prices for things like burger and chips are around €10 (£8) and the more premium steaks are more like €20 (£16). There is also Cantina Amigo at the Camp Resort, next door to Silver Lake. It's much cheaper - you can buy Bratwurst sausages, Chilli, basic burgers etc. with prices around €7 (£5.50) for most meals although it's far less formal.
The buffet restaurants at Hotel Colosseo, Hotel Castillo Alcazar and Hotel Bell Rock cost around €30 (£24) and the food is excellent and plentiful. Hotel Santa Isabel also has a buffet but this is more premium, costing around €40 (£32). These prices exclude drinks.
The a-la-carte restaurants in El Andaluz (Spanish influence) and Colosseo (Italian influence) will cost you around €30 (£24) for three courses. The a-la-carte restaurant 'Captains Finest' at Hotel Bell Rock will cost you around €40 (£32) for three courses and is more suited to things like steaks and fresh fish dishes. The premium restaurant is Ammolite at Bell Rock which is Michelin Starred. This will cost around €80 (£64) per person and is absolutely top class, first rate - one of the best restaurants in the entire region let alone just Europa-Park.
