It may be cheaper if you fly Air Aran, the islands own airway instead of BA or others. I know they fly from Prestwick but must have other departure points
All airlines in the north west - including the Manx airline and BA - seem to be similarly high-priced for the length of time you are in the air. I wondered if the landing charges at Ronaldsway were particularly high.
Also depends if you are going TT week,first week in June when they really bump up the prices by Air and by Ferry.
Emerald Airways do flights from Liverpool for �18.50 one way. http://uk.airkiosk.com/cgi-bin/airkiosk/I7/181002i?JEM=2
My annual TT flight has cost �80 return this year,still cheaper then I was paying up to 6 years ago.