I disagree.. next you'll be saying not to pay more than 2K for a kitchen. While some companies seem to be charging 550 not all are... and the 550 stuff must be bottom of the range, in my opinion.
It depends on the quality... but I think 500 to 550 is very cheap, and I'd wonder about the quality, both of the wardrobe, carcase etc, and the quality of the fitting.
I'm not sure if people are comparing like with like, there can be many differences between different wardrobes, which can have an effect on the price... same as cars or suits, while there are cheaper versions of both, there are also higher quality, more expensive versions...