Allis nut, your not going to find any detach of either ground bearing or non ground bearing worth pulling home for that kind of dollars, if your hauling a D8 around you need at leat three axles to do it legally, maybe even a triple on the back of the truck as well. Like I said before I have no idea how much you plan to move it, how far or how often, but if your price range is 5-6k, just a suggestion here, but hire someone to move it for you, by the time you have the trailer, truck, permits, everything dot legal and the insurance, your yearly buget for just owning the trailer will be more than 5-6k, not to mention fines if you get caught by the dot, and I don't care how legal you think you are, they'll find something wrong and educate you big time on how they want it done.
I started with a deck over trailer, they are cheaper by far, it worked for years, till we slid a machine sideways off the side in the winter with an icy deck, not something I'd ever want to do again, even slid one sideways and down the ramps in the back and almost laid it over as it hit the ground, came off the tracks on one side as I was about to dive off the upper side and onto the trailer when it came back down onto two tracks, but it hung there a minute or two, I was sure it was going to roll over but didn't, my wife witnessed this the second time around and told me, enough was enough, she didn't want to be widow anytime soon, or ever have to load anything ever on a deck over trailer, she even refuses to pull one, just because when she gets to where she's going she'll have to unload or load it. I guess its what you get used to, or can take as far as mishaps and things going wrong, do deck over trailer work, yes, but your 3 plus feet higher in the air and you have the hinge point, where the machine transisitons from the angle up to the the level deck, all the weight is on the hinge as it tilts down flat on the deck, thats usually where things happen, it can slide slideways, or spin around depending on where the cleats on the track are located to the deck, if both sides are equal on the deck or if the deck itself is level, we load on a lot of sloped area's and that isn't a good thing, best advice I can give is to either borrow a trailer, rent one or hire someone to haul your machine and "you" do the loading and unloading, everyone's idea from the ground is different than it is from the seat of the machine. I've seen an older d7 go off the side of a trailer before, the guy didn't have a seat belt on and luckily it only rolled onto its side, if it went any further he'd have been killed, since the roll threw him off, I"ve seen combines go off the side the same way, the truck driver in the seat didn't get killed that time either because it went over the side opposite the cab and the cab was up in the air, seen another dozer a d5 go off and that smashed the operators hand and crushed it as it was under the corner of the rops as it went over and heard of several that were killed because they kept rolling, either into a ditch by the side of the road or whatever. It also depends on your insurance company and who's actually doing the loading and unloading and what machines you have, now on my insurance it made little difference, but have been told by business owners their insurnace went down when they went to detach trailers, not sure if its true or not, but I still have both styles of trailers, so mine wouldn't drop in cost.
As they say if I could back up time and do it over again, instead of a deck over trailer, I'd pay a little more and buy a ground bearing trailer, just for the added safety of not going over the hinge point and when that became too much grief, I'd later update to a non ground bearing trailer later on, but that's me, I don't like big machines or any machines going over the hinge point, in my terraine, and adverse climates and conditions, but if you live in a dryer area of the world, have level ground or always load on the level and have rops on every machine you own and are careful, it might make a difference to opt to a deck over trailer.
And for what its worth, I've slid mahcines off the side of me detach as well, but it didn't go far, I always load along a road so there's a driveway beside the level portion of the deck, not a ditch just for that reason, its never a fun ride no matter what machine or trailer you have at the time. Best of luck on whatever you decide or get