Apply for your moragage and get quotes is my suggestion as to get both back can take time.
To work out your borrowing at this early stage is fairly simple. Take the build costs per sq ft in your area and multiply by the size of your home. Add 30/60k for finishing (how lavish do you want your home) and then add 10 to 15%. Its very rough and ready but it gives you an idea of your budget.
For example:
Build costs in Cork €75 per sq ft
Size of house = 2500 sqft
€75*2500 = €187500
Plus fittings, €187500 + €45k= €232,500
Contingency is 10% = €255,750
So I would ask the bank for ~€260,00. Once you are through the initial mortgage process quotes should be back and you will be able to fine tune the application.