To echo what most have already said - us truck camper folks have specific needs and it can be difficult to find a truck on the lots built the way we need/want it. We factory ordered both trucks we have owned. It is an absolute myth you pay more to factory order. In fact, when you factory order, you are only paying for the options you want and not the ones you don't want! As others mentioned, we also went through the fleet department.
When you order, as the build sheet is being compiled, you can watch how each option impacts the crucial number - payload. Personally, I find the fancy trim levels way overpriced and they do nothing to help carry a camper. However, selecting the right options does (i.e.; camper package, higher rated tires & payload package, etc.) Being particularly selective on the options, can help you stay in your budget and maximize payload.
Good luck with your decision.