Most people will not be starting out with an unlimited budget when moving into photography as a profession. Even if you do have large sums of money it would only be good business practice to not over spend. Many people don’t understand that your images are more so impacted by the lenses you use rather then the camera you use.
Good quality lenses are often refered to as fast lenses as they are able to achieve wide aperatures of F/2.8 or larger.
The focal length of the lens you use is usually a decison you make based on the type of photography that you are wanting to do
Here is a rough guide on lens focal lengths and their main use to provide you with some direction on what you might want to buy or rent.
14 mm to 35 mm range lenses are generally used in landscape photography, for shooting architecture and landscapes as well as a good lens range for environment portraits and street and edgy fashion photography
50mm is often referred to as the classic lens and further described as the focal length that gives you and image the resembles how you view a scene with the naked eye. The 50 mm is often use for portraits and in fashion photography
85 mm is the classic portrait lens and also good for fashion
90mm to 100mm is often also found to be a macro lens which can be use for portraits or fashion images but is most commonly used for close up work be it products like jewelry or images of small subjects like insects that they can be photographed one to one
100 to 200 mm lenses are use predominately in fashion, for portraits- and in nature and sport photography.
200mm and up lenses are basically used for shooting sports and wildlife, in particularly birds.