Not sure how much you want to invest, but if you can’t find anyone to do it for you as suggested above, I’d suggest these for $50
https://www.harborfreight.com/14-gauge-4-amp-heavy-duty-metal-shears-68199.html
Using a hole saw, cut a hole close to the center of your 14” hole and start cutting with the shears in a spiral working your way out to your 14” size. This will give you the opportunity to get comfortable with how the shear works before making your final cut.
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