I'd recommend the book "The Sailmakers Apprentice" About $25 About the best investment I ever made for the boat. It covers repairs, sail making and design (which helps with sail handling as you can determine "what I have" and "how its cut") and canvas work.
I was truly amazed at what you can accomplish with a regular sewing machine and sewing palm.
As most on this forum know I'm big on self sufficiency (and saving money) cause if it breaks while at sea what are you going to do? (and I'm a cheap sob). This book gives you the ability to repair while away from commercial facilities. It is also much cheaper and faster to do it yourself. I'm thinking that a quarter sized hole would take about $.05 worth of sail cloth and about 20 minutes to "professionally patch" and a 15' seam on the leach is just the thread and about 30 minutes of work with sewing machine and possibly some hand work if the seam is over the head or clew reinforcement panels.
It is pretty easy stuff, really!