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It's entirely possible to sideload on iOS, all you need is an OSX machine and a free Dev account.

Practical, no. But possible.

And how do you sell an app to iOS users that don't have an OSX machine and a dev account?

You don't? To build iOS apps you need X-Code. So you need a Mac.

Where can I get a free OSX machine?

Same place you got your free iOS device.