Typical rental prices involve 3-500 euros per month for a 1 bedroom flat, 2 bedrooms is 5-700 and 3 or 4 bedrooms is usually 800-1200.
Pretty much all seasonal lets go through agencies and as such require 2 months rent as a deposit, and a further months rent as the agencies fee. So this is 4 months rent up front. Ok you get half (the 2 months deposit) of it back provided you look after the place and dont bail half way through the season but it's still one hell of an initial outlay! Obviously the more people you live with the cheaper this becomes, especially if you have couples living with you. I'd make sure you have a job sorted though before you commit to an apartment because if you leave part way through the season you will not get your deposit back as the apartments are contracted for 5 month leases.