At least you have a realistic idea about what a hauler bed costs, and what it will cost in the future going forward. It will only be more.
More thoughts, since you asked...
While it has been very nice to have some features of my custom bed, such as side box storage access, complete bed utilization, outside "lockers" without having to climb up into the bed, etc, there have also been a few challenges.
It is difficult to find bed accessories "off the shelf". From roll top covers to back flip covers to ladder racks to headache racks to even the mounting system for a B&W hitch, there is no orderable part number that fits. Once you go custom, everything else added must be custom too.
On the other hand, this provides an opportunity to design accessories that work better, work differently, or are better suited for ones' personal needs. And, what you have is not cookie cutter like everyone else's. But, there is a cost to this uniqueness.
The 450 pickup bed, being the same as a 250 and 350 pickup bed, is ubiquitous. Every accessory company out there has designed something for it, because the Ford pickup is the number one selling full size truck. So you can not only find orderable parts, you can even find used accessories on CL or eBay, from 15 years ago, that will still fit the 450 bed.
On the other hand, that's like everyone else. And you have wasted bedwall and wheel well space. And to access storage (when set up for a fiver), you have to climb into the bed to get at the center. But the storage box will be cheaper than the custom boxes of a custom bed.
More thoughts... on fuel range and capacity, balanced with storage space...
With the 550, you can have up to 105 gallons of fuel capacity, with ZERO loss of bed space. To be certain, let's say 90 gallons, because I'm unsure of the status of the company that made the 65 gallon midship tank. But I am sure of the status of one of this web forum's sponsors: Transfer Flow. They make a 50 gallon midship tank for the narrow frame 550 chassis cab, and that, combined with the 40 gallon aft axle tank, adds up to 90 gallons, plus a gallon or two in the fuel rail and filter, of fuel capacity BELOW the datum line.
The "datum line" is a reference line of the chassis in elevation view. Let's call it the top of the frame rail. That's below the bed. No big boxes of fuel in the bed to have almost 100 gallons of range, where you can buy known good water free fuel at a good price, and go as far as you need to go (1,000 mile range at 11 mpg).
You can haul the same amount of fuel in a pick up, but then you can't haul much of anything else, because you lose a huge chunk of storage space that you already didn't have due to the inherent inefficiency of a fleet side pick up bed. The pick ups don't have an aft axle fuel tank. And the midship tank in the pick up holds less than the aft axle tank in the chassis cab.
On the other hand, with the chassis cab, you'll have to find a place to store the spare tire, if you chose to carry one. Yet, it is a lot easer to pick up and roll a tire (say, to or from the back of your trailer, or, in and out of your hauler bed) than it is to hand carry 50 gallons of fuel.
The depreciation hit might be heavier on a hauler bed... or not. The market is narrower, less universally understood, and not quantified by Kelly Blue Book. With a chassis cab, you don't have a complete vehicle until you have it completed, and KBB only estimates values of vehicles completed at the original manufacturer. The F450 pickup is a known and common quantity, completed by Ford. The F550 chassis cab will be completed by a second stage upfitter.
On the other hand, that upfitter could be you! Find another F550 hauler with a dead and gone 6.0 or 6.4 that frustrated it's owner one too many times, and buy the truck not running, for the hauler bed that is on it. Sell of the old chassis you pulled it from for parts, and then have the hauler bed painted to match and mounted to complete your new '15 550, for probably 10K less than having a fresh bed built.
Lot's of different ways to go, but the main thing is to wait and see exactly what differences in engines that the cab chassis will have in 2015. Will there be more alignment between the CC engines and the PU engines? Will the CC engines get updates also, but different updates? Will it take another year of teething pains to manifest any design, performance, implementation, or reliability deficiencies with the updates?
Only time on the road by paying customers, not engineering test tracks, not magazine reviews, and certainly not radiant Ford press releases, will tell.