Here's a post with a list of some options.
Leading edge tabs, fold point reinforcement, and stretch strips. The cost of doing it yourself is small, the material is cheap and repair only takes a little sewing. You can also replace the entire leading edge with better material for a bit more work.
The cost of people doing it is the time and shipping, not materials.
Some kite people would do them, but I think they all stopped when patents expired and several good competitors all have better kites.
Doing it yourself is not difficult. You can make 9 or so strips of 1/2" webbing or dacron or similar and sew them spanning the mesh across the entire length. Not hard to do, sewing on the sail body, across the torn mesh, and onto the bottom edge of the LE. Fold point reinforcement is similar, about 2" across. Be careful to maintain the width where the mesh was, and to not sew across the leading edge to block the channel, just sew where the stitching already is. You can hand sew it or use a sewing machine.
Stretch strips need a sewing machine. You can use the same insignia tape sold for boats, just a half inch or one inch strip exactly along where the vertical spars go. The tape is cheap, and strong. After taping it down, sew it in place.
Use polyester or other synthetic thread, cotton will rot eventually.