Just back from my week in Montauk! Did some scouting for you guys. Best places on the ocean are Wavecrest and the Panoramic View which are about 3 miles outside the village. Oceanside Beach Resort is the only motel in the village that I would recommend. All should have good prices after Labor Day. If your into camping Hither Hills State Park has beachside camping for about $25 a night.c Although this is up 400% in the past 22 years, it's still the deal of the century if you can get a site. Summer rentals are 11 months in advance but you should get lucky in the off season.
Bob