Would helm of suppression cause a repeat effect to cost more

No — Helm of Suppression doesn't inflate the Repeat cost itself; it just adds its flat increase to the total cost of the spell once.

Repeat is an optional additional cost added in step 2 of determining cost, and Helm's "+1" (or "+1 Energy +1 Power" when Empowered) is a cost increase applied in step 3 to the spell's total (Rule 356.2 → 356.3). So a spell with Repeat costs: base + Repeat cost + Helm's increase — the increase isn't multiplied by the number of times the effect repeats, and the Repeat cost isn't raised by 1.

Same logic as the discount side (FAQ #11694): one modifier, one spell, applied once to the total. Rule 820.3.a — it's still played only once, so only one Helm increase applies.