3 years is too long. Sorry.
HV
I am no Dr. but I believe in 3 years the Vigamox might lose it's effectiveness. If it were me, this is one area I wouldn't cut back on because Vigamox is CRITICAL for your eye health after eye procedures. You don't want to kick yourself if your eye heals with complications.
I too am always tring to save money where I can, but I would do without a new pair of shoes, jeans, or something else instead...just my two cents. ;-)