Looks like you have found a camper you like and it's a good fit for your truck. It sounds like you should really enjoy the TT.
It doesn't hurt to negotiate, but it may be more worth while to try negotiating things you will need to hit the campgrounds as well as price (vs price only).
A combination of some of the items below could easily make up the price difference you see online (don't expect all of these).
WDH,
Brake Controller (if you don't have one),
Sway control,
Surge Protector,
30-15A adapter,
Fresh Water Hoses,
Water Regulator,
Sewer Hoses,
Portable Tote,
Propane,
Battery,
Level blocks,
Wheel chokes (maybe even X chokes),