try http://www.atlantisart.co.uk/ they are the cheapest I know of and they supply major museums, so not shoddy by any means, if you find some one cheaper please let me know. Their site isn't the easiest to navigate though.
Do you know of a good framer in Ireland as I may be having a show in Portarlington, where I'm from but I've lived in the uk for the last 22 years, later this summer.
check for Lions. I dpn't know about website but they'll send you a free catalog and they have everything one needs for mounting matting,framing and presentation.