As someone who used to run a Skynet portal and no longer does because it was costing me too much money: no, it's not funded by subsidy from minted coins.

Right now portals pay for the hosting of the files as a charitable service to the community. In the future, portals will charge users directly for extra features (with U.S. dollars!)

Some portals may be operating less out of charity, and more out of a desire to build mindshare about their portal in hopes of translating that mindshare into future revenue via subscriptions.