When I cast Hard Bargain with repeat and my opponent casts Hard Bargain in response, does it counter both instances or only one?

Ruling: Hard Bargain counters both instances because repeat is still a single spell even when the repeat cost is paid, so the whole thing gets countered unless you pay (2).

Nuances:

• Paying the repeat cost doubles the effect but does not create a separate instance on the stack
• The entire repeated spell is countered as one unit