Vlihada beach is definitely my favourite on Santorini because of it's tranquillity, position (one can enjoy the sun literally all day long!) and spectacular landscape.
However, I don't know who sets the prices for the umbrellas/chairs there but they vary day by day (?!). To be more precise, there are often big signs saying the price is 5 EU but then someone comes and charges you 7 EU. When you complain about that discrepancy pointing at the sign, the answer is "I'm sorry, it's 7 EU" with no reason given.
I really don't mind paying that price and I don't think it's expensive at all but this is definitely not the way to run a business. So will you please make up your minds and get serious about it because nobody likes to be tricked, particulary if you make it so obvious.