Good laptop for little money (for office and programming)?

I need a laptp sufficient for programming and Word, Excel, PowerPoint, etc. He should be slim and not cost more than 400 euro. Better would be 250 euro - 300 euro.

I'll say so - you can definitely present something for that price, but you will not be happy with it in the long run. Your programs will need RAM, what I have found so far are max. 4GB of RAM for the price up to 300 euro. Not really enough.
In addition, who buys cheap, buy bad - especially in technology. Try to increase your maximum price (500 euro upwards) - so that it really pays off for you.