If you find a model you really like, shop around some on the internet and near you. Search for that model and see what other dealers are selling it for. Be aware also that Jayco owns Starcraft, and Forest River makes both Flagstaff and Rockwood (they are twins, but different cosmetics and model numbers), so you can cross-shop that way too. After you've done this, you are equipped to negotiate with the dealer or dealers you'd prefer to do business with.
Of course they want to sell you what they have on the lot, because they're paying interest on them and it's an immediate sale versus waiting 2-3 months for your ordered unit to come in (and then they finally get paid... if you didn't change your mind in the meantime). Nothing wrong with you ordering something exactly the way you want it, but of course it might come in too late for you to use this year.
It's strange to me, the prices of stuff. Back in the late 90s I bought a new Starcraft popup for $4500; pretty much any travel trailer would have been more than twice as much, and I couldn't afford them. Now I see plenty of popups selling in the teens, and I could buy a basic 16' lightweight TT for about $11K.