As a result of your inquiry, you will decide whether you are likely to get what you want, or not. If you are uneasy, write to a freelance researcher. One would hope your Society keeps a list of those accredited by the professional bodies for Ireland and Northern Ireland. If not a list is available from Genealogical Office, Dublin 2. The better freelancers are familiar with a broader range of records than some centres and may offer a better service for certain areas.
Access is almost always free.
That is the way they were set up. If they have what you are looking for, you are welcome to use it. Published sources, like Griffith's Valuation, Trade Directories, Alumni of Dublin University or the Law School in various places. You go where the record is kept. The whole concept of the Research Centre is quite different.