It’s simple: supply and demand. Most legitimate booster sites seek to hire players who are ranked Diamond or above. They do so because it puts their customers at ease, yes, but also because diamond-level skill is required in order to be able to consistently and systematically boost accounts to the customer’s desired rank.
Diamond players, however, are rare. According to the League of Graphs, only about 2.5% of players worldwide are ranked diamond or higher, and only a tiny minority of that 2.5 % will be willing and able to offer their services as boosters at any given moment. Especially since boosting an account may take upwards of two weeks in some cases, with the booster playing six to eight hours a day, which makes them unable to work on other projects for the duration of the boost.
When you take all that into account, it becomes clear why some elo boost jobs packages cost several hundred dollars; they cost that much because they require highly specialized labor and wouldn’t be worth the booster’s time otherwise. You can learn more about elo boosting services by visiting this site.