When someone is selling in a limited market, what % of new do you offer?

I am looking to purchase a new wakeboard tower. My boat is a 2009 model and the model design changed for the 2010 models. I purchased it from someone about eight months after he purchased it new. It had only 6 hours on the boat, but no tower. I saved about $12k off a new boat price, though. Screw that 1st year depreciation. I'll never buy a new boat!

Now, I want to get a tower. There are decent after-market towers out there ranging from $1200 - $2200. However, I found someone local who was in the tower installation business, but now he's getting out of the business and he has a new OEM tower available to get rid of. If ordered from a boat dealer, the OEM tower is $2500, plus shipping. This guy is offering it for $1800. That's not a bad deal, but as he is going out-of-business, I feel like I can get this for less. This isn't something I "have to have", so I feel like I can play hardball on this, but also, I don't want to be so low on my offer that he ignores it and doesn't counter-offer. Since it's for an older boat (2009), he has a limited number of local clients who might be interested in spending this kind of money for an upgrade to their boat. He's been advertising it since January, initially trying to get $2200, then waited until March and drooped it to $2000. Now, here is is May, and he's asking $1800.

What is a reasonable percentage off retail to offer under these circumstances?