If you had a more rounded out menu of services to be offered it may be possible to make enough for drinking money and maybe a new toy now and again. I would not recommend it as a dependable source of food
money or equipment
money but you never know.
Once you get a feel for the different boats and what their characteristic problems are, you may be able to "talk-up" business to fellow cruisers. I've seen one really thin guy and his son do a thriving business doing work up masts, changing out lights for LED's (generally entire units not just bulb), new halyards for some of the boats where it is difficult to do without going up the mast
, replacing zincs, even selling emergency SSB antenna
you haul up with halyard
, installing WIFI
boosters at spreaders or top of mast
Generally things many of us would rather pay for than do ourselves due to lack of specialized equipment
, age, weight or prevailing conditions.
You would need to be careful in many places as this may not be very legal
. Lots of places require Work Permits for non-citizens to perform any work for pay or other consideration. In the real world, among cruisers "things" can be worked out but you don't want to become too obvious which means that even good recommendations can land you in trouble.
BTW I've had my bottom done for $90 in BVI which was less than what some charge.