I made my own holdback stakes using $2 worth of stuff from home depot. You'll need one 48" wooden dowel, get the one thinner than a broomstick, but thicker than a ball-point pen (should cost 94 cents); a 6' length of foam pipe insulation (should cost 79 cents); and some duct tape that you'll have laying around.

Cut the dowel in half, cut it at a 45 degree or more angle so that the ends are pointed. Tape foam to the "flat" ends, allow at least 7-9 inches of dowel not covered with foam.

When you get to the field, push your stakes into the ground about 3-5 inches apart (depending on model). Make sure they go in at least 6 inches or so. Put the tail of your plane between the stakes, make sure that the tail is in contact with foam and not wood, and you're all set.