If you go to HIA.ie website you can see the current price of any plan, but it is not reliable if say your renewal date is 2021.
Current HIA price is 1265 per person so that's 2530 per annum.
If you go onto the Laya website, you can see prices up to 30 days ahead.
I don't think there's any negotiation... some people try to avoid future prices increases by basically cancelling their current plan a day early and renewing from e.g. December 2020 rather than January 2021. But I haven't executed that maneuver myself yet.
Also, the credit charge is not something I have come across, paying directly for health insurance or via employer.
So maybe you have scope there with the employer payroll.