The form 8621 is not a stand alone form that can be submitted without the information from the rest of your tax return. Since there is income that may need to add to your tax return the form needs to be included with your filing.
You can only chose to pay later if you are going to receive a refund large enough to pay the TurboTax fees and you efile your return.
You can pay for the return and then you can download and print the return and mail it to the IRS.
Yes, the full TurboTax fees applies as efiling is not a separate fee.
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