Hi Eric and Elena,
I'm one of the sailors who is contempating a move to power - not really for livaboard use - but so to allow us to travel up rivers and canals etc and give us a few new challenges in life.
All the others give good advice but certainly over this side of the Atlantic, our research
shows the cost per square foot of boats (same age) would currently put power as better value.
In terms of costs of maintenance
/ motive power, it is my view that provided you buy a displacement
power boat (that chugs along around same speed as a sailboat does) and that the engine(s) are in good order, then the monthly cost would work out around the same. The $ spent on a new set of sails
can fill a lot of fuel tanks
And finally you'll get a lot more useful space on a 40 foot power boat than a 40 foot sailing yacht.
Lots to consider - enjoy your own research
and we all look forward to hearing what you buy.