You'd be surprised, home prices are actually going down so it is possible to buy a decent house in the $600k price range. Some areas I would suggest are Hawthorne, Dobbs Ferry and Eastchester. Good schools, close to the train, nice neighborhoods.
Check out
Moderator cut: no real estate agency specific sites please if you want to do a search for homes by school district or town. You can also check the Westchester Board of realtors website (you do not have to be a realtor to see listings.
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Good luck.