600 is going to be tough, even out here in Milford area.
There is a nice apt complex in Goshen NY that does short term rents, but the rent will run more like 1000/month.
Have you looked up the Times Herald record?
http://www.recordonline.com ?
They have classifieds for a pretty large area of the Hudson Valley.
Might want to think about Guardian Self Storage for some of the furniture, makes things easier not having to trip over yourself in a small apt.
Ellenville is kind of out in the middle of nowhere and it is a PIA to get across Wurtsboro mountain in the wintertime..might I suggest you look at New Paltz instead? Or even Wappingers Falls? They have 3 different apt complexes. But your target price range is going to be tough to fill..
Good Luck!