It looks like quadratic growth until around 2011, after that it becomes linear. This still seems like a lot of growth, considering the number of pageviews per article seems to be roughly constant over the last 5 years [1]
0: https://wikimediafoundation.org/about/financial-reports/
1: https://tools.wmflabs.org/pageviews/?project=en.wikipedia.or...
Edit: this is how last year's expenses break down:
Salaries and wages: 46,146,897
Awards and grants: 12,653,284
Internet hosting: 2,335,918
In-kind service expenses: 1,361,958
Donation processing expenses: 4,977,583
Professional service expenses: 8,998,261
Other operating expenses: 9,005,744
Travel and conferences: 2,867,774
Depreciation and amortization: 2,856,901
Special event expense, net: 209,690
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Total expenses: 91,414,010
(sorry if that's unreadable on mobile)