Financial sense, car loan and newer car don't go in the same sentence.
Most buy new cars because they want a new car, want the newest model or change of need or image. If you want to keep depreciation to a minimum then as DaveD says, buy second hand (thereby already saving at least 20-30% of the initial depreciation of driving a new car off the forecourts), import from mainland UK (where cars are even cheaper than the north because of the pure scale of the second hand market), look for low miles, conservative colouring of car and a prestigeous brand (the Germans and Honda) and sought after engine/ engine size for the model.
Yes importing may require a touch of manoevering however that's the beauty of the internet- target a area of UK/ N. ireland, do your car searches online going specifically for the car/model and spec you are after (you'd be doing this anyway in Ireland, plus you'll find UK cars are better spec than Irish), and check the VRT for that car online or ringing the VRT office. Once you've seen a selection for the car you want then arrange a couple fo days to visit, look and test drive the car, Barter hard for the car you pick pricing dealers against each other (much easier to do in UK than in Ireland where dealers for some reason are arrogant) arrange temporary insurance over the phone with the dealer and drive it back to Ireland via the ferry. If you are married, you can look at the cars while the wife/partner goes on a shopping trip...everyone happy. get home, make appointment with VRT office, get your plates and fully insured in a couple of weeks. Obviously if you're gonna be saving a few grand then this is very worthwhile doing. Don't be put off by resale value (no effect in my experience). I've mentioned before that when i moved from the UK, I brought my mini with me. I sold it easily last year actually getting more money for it than I paid originally 4 years ago....obviously I didn't pay VRT in the UK, but just saying it doesnt affect the value of the car.
Also, importing cars from the UK is what most second hand car dealers do...I've been to a good few in my time and you'd be amazed how many UK reg cars they have now sitting waiting to get their VRT/ irish plates....car dealers know this is the best way to make a profit.
Nothing more frustrating I'm sure than spending a number of weekends driving around Ireland looking at one car at a time.