Plan B,
Take the old alternator with you to the parts store.
No temporary core charge needed since they already have the old one. 
But core charges are zero worries mate.
just take back the old one…in the box it came in…and get your refund.
–super simple, a daily business method 'round here.
If you use your debit/charge card you’ll never see the extra, it will be a wash-out on you statement.