Similar to Mozilla & Firefox, there isn't an exact breakdown for Wikimedia expenditures to know the costs associated with Wikipedia. For Firefox, it's often stated its costs are ~200m but those are all expenses Mozilla categorizes under software development. For Wikimedia, within their operation expenses, ~3m were in hosting and ~84m in salaries (related to programs). The salaries are stated to be for multiple initiatives, among which platform development is mentioned*.

*Although arguably the most important part of Wikipedia, and their other collaborative projects, are the volunteers maintaining and contributing to it, rather the developers.