The Mohonk Preserve does not exist solely for the sake of climbing, nor outdoor recreation in general.
I suppose many don't care so much about the animals and plants which have a chance at future survival because of the environment the preserve affords them,but there is a bigger picture to see if one is so inclined.
I know times are tough. I am living on less than $700/month, and my membership will be due in a a couple months, but I will pay it without complaining. $17 a day? Yeah - it DOES seem expensive, but.... next dinner out, add up the cost. For a lot of us, we will spend more on that meal with drinks than a day at the preserve. Or - think about our last gear purchase? 3 new biners (do we REALLY need the latest micro biner????) is more than a day pass.
You can also use your preserve membership to gain access to many nature preserves throughout the US. Link: http://mohonkpreserve.org/pdf/ANCABrochure.pdf
Really - I encourage people to buy a membership and look at it NOT as just the cost of climbing, but as a donation that helps the world to be a better place.