Air Southwest will be flying from Dublin - Newquay this summer -
I was going to say it's probably a good be more expensive than Ryanair to Bristol.. but actually it's a bargain... €54 r/t including taxes ... that's a good deal I would say .. especially if it avoids a 3 hr drive from Bristol
Which part of Cornwall are you going to? It's a pretty big place and can take hours to get around. Ryanair fly from London (I don't know which airport) to Newquay so perhaps you could hop via London.