As for cost your local m/c repair shop might be able to give you a ball-park figure.
If it were my bike I would buy a replacement control switch and fit it as being the most likely cause.
It may be a bad connection - it may be the flasher unit - clearly it's something that comes and goes - wobbling the wiring might bring the fault on - then you'll know better (maybe) if the connections are good or not.
Switch - Flasher - Wiring - one of those
Good luck...
January 2015