Compared to Europe the price level in Sri Lanka is cheap. The whole country is easy to travel via public transportation (supercheap but you need more time of course), or hiring a driver for your own (around 700 USD for 2 weeks) – I would not recommend to rent a car by your own, as the traffic in Sri Lanka (especially in the bigger cities or villages) can get pretty chaotic.
Normally you will pay around 10-20 EUR/person per night for a normal/basic accommodation double room (so when you have a second person). For a breakfast (which is sometimes included at the accommodation), calculate with 4 EUR. A lunch/dinner will cost you about 3-10 EUR, depending on what you want to pay, or what type of restaurant you want to have.
In Kalpitiya generally prices are higher than in rest of Sri Lanka – I think because of the (currently) not so touristic amount of options the current level is a bit higher. In the village Kalpitiya itself, you can get things cheaper, but there are not really many restaurants with European/western standard.