We advise you to be more careful about these travel agencies. Tour price is a very important factor that most clients care about. However, please do not only judge the tour by comparing the price.
Just like an old Chinese saying: the higher is the price the better is the quality of the merchandise. Some operators offer quite a low price, while they are unable to provide an international standard service. Even worse they will not meet your expectation, or maybe put you into a shopping tour.