Ok I've only gone to the Elara site so far and I've gone over your budegt by 50 euros because I selected a 104 euro SSD, if you remove the SSD and use a normal hard drive or an existing hard drive you have it will come in under budget.

Now what you could do is comapare the same components on the other sites to see who is cheaper. To assemble the system for you I don't think they will charge much. It's a kickass build by the way, you could always add a dedicated GPU in future if you wish as the PSU is more than enough.