It costs roughly the same amount ($50 for an individual, $100 for a company) to purchase a developer license that can submit apps to the Windows 8 Store. Furthermore, the Windows Store also has restrictive terms on what is acceptable, and does not issue refunds for developer accounts when your apps don't make the cut.
You cannot install Windows 8 metro / modern UI apps from anywhere but the Windows Store without unlocking the device with a developer account.
You cannot install Windows 8 metro / modern UI apps from anywhere but the Windows Store without unlocking the device with a developer account.