You can fill a prescription in the North for a fraction of what you would pay here on certain meds (particularly those that are no longer under licence).
You can ask your GP to give you a 6 month script with the generic name of the drug and can fill it at any pharmacy in the North.
I found Boots to be the cheapest and easiest to deal with - I was paying €30 per month in the South for my meds and €90 per month for my husbands. I got a full 6 month supply of my meds for UK£12 and 6 months of my husband's for a total UK£120.
That's a saving of approximately €560 for six months.