Cost is a function of time. If you want a simple site that will take little time to develop, it will be cheap. If you want a regulation compliant industry-specific platform it will be expensive.
You can hire a dude on fiverr to make 'Something' for $5. You can hire an amazing designer to make something very nice looking, but technically simple for $50,000. Set a budget, decide on you priorities, build a spec for what the website/app needs to do (start with MVP, the simplest version that serves the purpose) and go from there.
The cost range is extremely wide. I charge $500/hr and typically sell my time in blocks of 40-80 hours. Others will quote you a fixed price to deliver a particular spec.