If I play Hard Bargain and play its repeat cost when my opponent defy's it, does it also counter the repeat cost?

Yes, if your opponent uses Defy to counter your Hard Bargain, it counters the entire spell, including the repeated effect.

According to RiftJudge FAQ #10472 and FAQ #10774:

1. Repeat is an additional cost: You must declare and pay the Repeat cost when you first play Hard Bargain from your hand, before it is finalized onto the chain.
2. Single entity on the chain: Even when you pay the Repeat cost, Hard Bargain exists as a single entity on the chain. It does not create a second, separate spell.
3. Defy counters the whole spell: Because Defy targets the base spell, and the entire repeated effect is part of that single chain item, Defy successfully counters the entire spell. None of the effects occur (including the repeated ones), and you do not receive a refund for any costs paid, including the Repeat cost (per Rule 425.1.c).

In short: you cannot split the effects to counter the Defy, and paying for Repeat does not protect the spell from being countered.