that the diphthong "ei" in Welsh does not have an exact counterpart in English. It would sound something like a schwa ("uh") followed quickly, almost blended with, "ee." Like: [Uh-ee]-ra. Personally I would prefer to write this as OY-ra. But that is not exactly correct, I don't think. Check out the soundfiles for the diphthong on the site, that should give you some idea.
In English, I believe it's just like the name Ira, with a long I as we're used to hearing in Eileen.