I have yet to find anything that is as inexpensive and as easy to apply as RainX. Its always lasted long enough for me. If you have an issue, use the RainX windsheild washer fluid and that will act as a booster and keep the RainX working well.
this x10000...i last applied rain x to my windshield in my last semester of college. i've been at my job for about 2 years now. still working great on my windshield.