Stumbled upon Ohloh a site that values open source projects; the algorithm is based on Constructive Cost Model (COCOMO) II.

I thought I would add up the cost of the stack, the core applications we run and the extensions/plugins available to us.

WordPress: $2,120,767

MediaWiki: $49,274,441

Linux: $173,253,811

Apache: $14,913,508

PHP: $44,546,186

MySQL: $21,388,883

Total: $307,751,855
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WordPress / MediaWiki Extensions and plugins

(would be more if you included the Git repo projects where some developers chose to host now).

WordPress Plugins: Estimated project cost: $2,254,259

MediaWiki Extensions: Estimated project cost: $2,679,586

Total: $4,933,845

—————————-
Grand Total: $312,658,700

*Would be considerably more with inclusion sub projects like jQuery , Python , node.js, PHP modules etc.

Thank you Open Source community.