1) sell the trailer to me. I have a vermeer sc252 and would like a trailer.
2) Ebay will almost suredly get you the lowest price for your grinder. Good for a buyer but bad for a seller in my opinion. Try regional equipment sales magazines or newspapers - I've had great luck with a local farm country trader that carries everything related to ag industry equipment.
3) If he won't pay up front for the travel expense, forget it - especially if you're not going that way anymore. I'd consider meeting half way for free if the selling price was right. If he's willing to spend the time and cost of meeting you half way, you know he's serious.
Better yet, try telling him you'll sell the machine for $5700 and give a $300 fuel allowance FOB your location rather than the full $6k and you spending a day on the road delivering it half way...