Living aboard a boat will cost about the same as living on land. If you have a big boat it will be the same as having a big house. A new house will cost less to maintain than a old one... same with boats. The only advantage may be property tax or lack of. So Ken, you have answered your own question.
CapnTerral: a 25 foot sail boat is more like camping than living aboard. Maybe consider a little bit larger boat.