if you look at the numbers raw it might be salary for a week but assuming your developer has stuff on his/her plate and this stuff actually will make you more money in the long run (why would they be employed by you otherwise?) its more than their raw salary and the cost of hardware and rent. opportunity cost.
I'm familiar with the concept of opportunity cost, but the question of whether to build or buy is highly context-dependant. As is so often the case in software development: it depends. Not all B2B tools are the same. Not all integration efforts are the same. Not all developer hours cost the same. Not every return on investment is the same.
