(i will admit to not having read beyond the first half dozen posts, so feel free to ignore if this has been suggested already)
if westchester has the best flight deals, but parking is the deal-breaker, consider finding a "park/sleep/fly" hotel near westchester... even if you don't "sleep" the cost of one night of lodging may be considerably less than ten days of parking at the airport... it's definitely worth a look-see... we had great luck with this when flying out of pittsburgh a few years back...