You've got a few main options for building your web app.
You could go with an agency - they're the complete package. You get project managers, designers, developers, the whole crew. Downside? They're not cheap. $50 - 150/hour, depending on where they're based. But if your project's complex or you don't want to manage everything yourself, that structure can be worth it.
Freelancers are the budget-friendly route. You're looking at $25 - 100/hour, sometimes less. They're great for smaller projects or if you've got an evident vision of what you want. Just know that you're the project manager here, so it works best when you know exactly what needs to be done.
Then there's hiring your own team. That's the "we're serious about this" option. You get total control and people dedicated to your product, but you're talking $80k+ per developer, plus benefits, equipment, and all that. It only makes sense if this is going to be an ongoing thing.
Whatever direction you go, don't skip the vetting process. Look at their past work - specifically, stuff similar to what you need. Talk to them about how they communicate (this is huge, trust me). And make sure there aren't going to be surprise costs halfway through.
We are happy to examine your specific project to determine which route makes the most sense for you. Let's Book a Meeting!