Hi Bemmi,
Think the cost for top and bottom teeth is around €4k with 20% back in tax. I think its around €1000-€1200 cheaper up the north and you should also be able to claim tax back on this.
You need to way up the cost of traveling up every month or second month for maybe up to 18months. Along with petrol costs of getting there theres also the time constraint and whether you need to take time of work and your daughter needs to take time off school/work depending on her age.
I know there is alot of deals on
www.mad4deals.com for dentists one recently was for braces but that deal is finished. So its worth keeping an eye out on the site. I was also at the RDS wedding show and there was a stand for a dentist who was doing €750 off braces treatment.
All in all I would say keep an eye out for deals as alot of them are looking to get business. I am not sure were you live but you could look at
http://www.balbriggandentalcare.ie/pricelist.html I know a few people who have had crowns and fillings out there and the service is great plus the price is reasonable.
Hope this helps but make sure you shop around and get plenty of quotes.