What I'd do.
Remove battery from car. Take to battery selling place. Have them charge and load test the battery (there is a specific "tool" to do this. About $100 to buy a good one.) and if bad, you replace the battery. Worst case you pay for the charge.
You don't need a Porsche battery, one under $100 would do. List of batteries known to fit is on my site.
Link also discussion on how to test a battery there.
Replace battery with a charged battery and try to start. If that fails, then replace the ignition switch.
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