Mike is right. It rarely is cheaper to build your own solution versus taking a product that someone has already written and configuring it for your environment. It will depend quite a bit on the needs of the company and how well the third-party products can meet them without customization. It will also depend upon how complex the solution is.
To put it another way...the third-party vendor is going to have a team of architects and developers who do nothing but work on the product, do bug fixes, and add features. That development cost is spread across their entire customer base, not just you. In order for you to make something comparable, you would need to employ teams of architects and developers, but you have no customers to spread the cost across.
In my experience it's usually only a good idea to build your own application if at least one of the following is true:
1. None of the third-party solutions available meet your needs.
2. The resulting solution would be relatively simple and specific to your environment.
3. You are regulated in a manner that requires you to actually own/have access to the application source code (very common with government agencies).
4. You already have strong software development skills and practices in-house.
If an item from 1-3 applies but item 4 does not, then you can contract out the development of your software. I work for a company that does custom software development (amongst many other things). You can get most of the advantages of developing the software in-house, without having to worry about as many of the nitty-gritty details, and you can work out the terms that make the most sense for your company in the contract. The potential upside here is that a company that specializes in custom software development like that will most likely have a staff with skills that are very current in the latest technologies, as well as project managers, user experience designers, etc.
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