I pretty much agree with everybody that it's at least $100 overpriced. And I don't want to rain on your parade, but I'd be surprised if a dealer would agree to a straight up trade for a 6" model. They don't seem to be as popular, so it might not be as easy for him to re-sell, at least not at that price. If it were me I'd go there with cash in hand and make an offer. Start at $500, knowing you'll go to $550. Yeah, I know, it's still a bit too much, but in a few years you'll still have the Highway Patrolman. I doubt you'll still have the $550.
Let us know how it turns out, Pastor. God is on your side. (And I like the fact you still have Sunday night services, God REALLY likes that). I was raised Baptist and remember those days fondly.
Now excuse me, gotta get my suit on for church.
Jim