What is the cheapest easiest way to fix a tear in a kite? Will tape work? What kind is the best to use if so? I noticed an approx. 10" tear on one of the seams of my small PL water foil kite on the back (non-birdle side) side of the kite.

Fixmykite.com has a great reputation here. Send it to them and they will fix it.

Cheapest way (not the best way) is to take a needle and thread and sew it up by hand, or if you have a machine, sew it up with the machine. I sewed up a tear about 4" in foil kite that way and it work great. Seems like 10" is a lot to expect tape to hold.