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Maybe just hire a data engineer or two to start. They could potentially deal with the pain points and make life easier for your team. A lot of data engineering these days involves glueing various services together and managing the data flows between them. So an experienced data engineer should be able to do what you need.

Overtime, you could move away from the software in question as various functions are replaced with other services or internal code. Or if you realize that replicating the software in question would be too prohibitive, at least you have some folks that are adept at dealing with that type of stuff.

It is worth mentioning that when managing software projects, the complexity and frustrations tend to sneak up on you. The first prototypes tend to come together fast, and are nice and clean and crisp. But overtime, the feature set grows, the complexity grows, and the cost and time it takes to iterate grows. If you only need a very small slice of the features of the software in question, and you are paying an arm and a leg for said software, then it might make sense to roll your own. But it is easy to underestimate the complexity of what you need accomplished and rolling your own could end up being a very costly mistake.