I have done some more searching...
http://www.luxair.lu/en/ will do Manchester to Dublin return for £89.80 each including taxes on those dates in May.
Aerlingus will do it in May on those dates for £78.40 each including taxes.
British Airways will do it for £109.20 each, including all taxes.
(Guess who did a late shift today and can't relax enough to sleep yet?lol)