Lakeside Farms in Ballston Spa has a lovely pavilion and field space. I went to a wedding there (thrown by a thrifty couple) and it was very nice. You could also consider a pavilion in Spa State Park or at The Fish Hatchery (by Echo Lake) in Warrensburgh, NY. Burlap and Beams is a nice space in Thurman, NY, though I'm not familiar with their pricing.
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