This strikes me as an amazingly rational approach to build vs buy. Including trying to estimate the entire cost. A solution you build yourself costs more than

This strikes me as an amazingly rational approach to build vs buy. Including trying to estimate the entire cost. A solution you build yourself costs more than just the time of the engineer to build the first version, the work revolving around maintenance and improving it, when that could be borne by an outside company, could be quite high. Also, when an outside company makes it, they can amortize the cost of a new feature across multiple customers. And people will often build things that work with that product, saving you even more effort. The cost of buying though, is also of course not just the money you pay (free and open source still have a significant cost). How complex is the bought system vs the one you would build? How hard is it to replace with something else? How well tested is it? I've done the 'buy' approach with some open source things and services before and super regretted it when it took longer to debug than writing my own and maintaining it would have.