Adrian,
The problem is that no-one, not even the Mormons with their massive world genealogy project, seems to have copied or indexed the Irish Protestant records; so where they still exist, they reside only at the church itself or its successor church. Since most of the 19th-century Protestant churches are now gone, it is quite a project just to find out where the records currently are, and the only way I have found to get copies is to write to the church, send a donation and ask some-one to make a search of the records. I have not been able to find any of the church records of my family in South Dublin; I don't know which church they attended (or even whether they were Baptist or Presbyterian) much less where the records are now. My Irish relatives have been unable to find them either. Some of the local heritage societies have copies of Protestant records, but their charges are so high that I haven't considered them except as a last resort; they want a large fee just to say what records they have, so I expect their fee for actually searching and copying those records would be substantial.
One fellow researcher told me that she found it cheaper to fly to Dublin and search the records herself, rather than pay the fees of the heritage society or a professional researcher. Which is probably the point; the Irish economy depended for many years on genealogical tourism. If you know of a better way of researching Irish Protestant church records, please let us know!