Here’s how a real graphic designer sees this… you obviously are not capable of doing whatever graphic work you need yourself. You’re not only paying for ability, you’re paying for time and most likely concept as well. Fact of the matter is, we don’t know how long it will take because of a multitude of variables and there will most likely be changes directed by the client which… will take more time. Bottom line - unless you’re using an amateur designer or someone just starting out, you’re not going to get a flat rate. Personally, I charge a high initial price and a lesser price per proof for revisions. You seem more interested in cost of quality, so I’d just stick with fiverr… haggling with designers over what they charge is insulting.