Have you ever been in the position of quoting for a job? Not easy when the client doesn't really understand what they want and they certainly won't tell you what they want to spend.
I try to explain in terms of film production. Whether they want the full film crew or a bloke with a video camera. They could both film the same thing but the results would be dramatically different. Of course the answer might be that they want the result of the full crew for the price of the bloke with a video camera.
The point is there is often a low cost solution but it probably won't do quite what you had in mind, and it may well cost you a great deal more than you saved when it fails to perform the way it needs to.
So it is worth working with your developer so you both understand the budgets and the requirements at the outset.