I have heard that question quite often in my life. How much would it cost to build this application?
At the very least, it would be necessary to provide mockups to estimate the time it would take to implement it. For relatively simple applications, mockups would certainly give an idea of what effort it would take to build it. But then again, not always. For example, what would it take to build this?
The system behind these two pages is now worth almost half a trillion dollars. Therefore, there are good reasons to believe that it will not be possible to replicate it for a few thousand dollars. Otherwise, everybody and their little sister would be doing exactly that. Mockups are a necessary condition for getting an idea of what the system will be doing. However, mockups are often not a sufficient condition.
The reverse is probably also true. If it is possible to describe an application by just showing its mockups, it is probably not worthwhile building it in the first place. Without invisible part that makes the business model non-trivial, the application will be twelve in a dozen. Everybody and their little sister will be able to replicate it. There will be no competitive advantage for the platform. In other words, it will never make money. My advice: stop wasting your time and your money already.
Thinking in terms of a budget to build an application, is usually not a good idea. If the team which built the application, moves on after completing it, who will be fixing issues or adding necessary features after that? I have experienced situations in which there were no backups of the application and in which nobody was able to re-install the application. The system was just one disk failure or one successful attack from the internet away from getting lost.
An application is something with a yearly budget, and not something with a one-off budget. An application should always be part of a business model, just like any investment. Furthermore, if the budget matters, the application probably doesn’t. Who cares how much the initial budget was for WhatsApp, Facebook, or Google Search? That would be a total non-issue. It would probably be the most irrelevant question ever.
It is much easier to find developers to build a new application than to find developers to take over an existing one. Lots of companies find themselves in the situation that nobody can or wants to figure out how to fix their undocumented application.
This is also why I find it so funny when prospective clients play hard-ball on price and hourly rates. Six months later it will cost nothing to the developers to move on to another project, while the client will be sitting on an incomprehensible black box that nobody else understands. At that point, when the original developers leave, the client loses a good part of his investment, if not everything. The tables will turn very, very soon on hard-balling clients. It is simple. You cannot go to the market to find people who can do something that you cannot do, and then hope at the same time to outsmart these very people. That strategy is too contradictory to ever be successful.
The right kind of clients have a knack for making money, usually already have a lot of it too, know a specific domain and/or client base really well, and most importantly, do not hesitate to share the dough with you. Only then, we are talking about a win-win. Most prospective clients are not win-win. Ignore them. They are a waste of time.
Like most developers, I am not looking for clients (or even employers) right now. Sometimes I am, but that happens once in a blue moon. When occasionally looking for clients, just like in any other on-boarding situation, proof-of-work (PoW) barriers are important instruments to spare yourself from dealing with the wrong crowd. So, my first question to a prospective client is always: Where are the mockups? No, I am not going to create them for free. And no, I am not even going to create them for a fee. I could help you finding the right person to do this and work with you on his deliveries, but you will, of course, have to pay me for my help. If it even gets to that discussion, instead of the usual <ctrl> + d key combination for “delete”.